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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Wed 08, 2020 6:30 pm 
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devilsmist: Incoming RF? How does that get past the power supply? I actually saw the signal improve on my oscilloscope from when I started. The waveform lines were thick, indicating noise, but were thinner and more intense after I was done.

Jim Mueller: Please elaborate. They're important for what? Something besides what devilsmist said?

pixellany: Thanks for the reply. Really? The point-to-point mess I see in the chassis of AM/FM tube radio's sure made me think otherwise, but I admit I don't have FM receiver design experience. Is moving leads around an issue you have had to deal with over the years?

Like I said, I needed my 324 to do an alignment so I stopped working on the RF cathode follower once I got it just a little better and sharper. I left a .0015 in there for the B+ RF blocker, C5 (original was .001) for now. It made only a small waveform difference, but it was new and not leaky so that was probably more of the improvement than the 50% value increase. While that nasty waveform still bugs me, I have lots of tube radios to work on and even more tube amplifiers to build.

My oscilloscope only goes to 60 MHz (and it is really petering out before then) so I don't know what the 145 MHz signal strength is, other than it is strong enough to trigger and display a constant frequency on my Heathkit IM-2410. So all I know for sure is that it is there.

Dale H. Cook: Now YOUR reply is intriguing. There is a fundamental issue with service-grade equipment that makes it which? Impractical to upgrade or nearly impossible to upgrade? Your lab-grade signal generator is awesome looking. But does it really take that level of equipment to get a cathode follower to not distort its input? Now you guys are going to get me back into that 324 instead of working on my other tube stuff!

You mentioned that I might not have the experience to work on lab equipment. I hesitate to give my background in a post, but I also don't see anywhere in my profile where I can put it. Did I miss something? Shouldn't each of us be able to at least put something into our profile so other members can tell at a glance if they are replying to a newbie or a very experienced electronics technician? You have some info in your 'Occupation' field (BTW, interesting that you specify "instrumentation" rather than leaving your interest generic). Should I put all my years of experience there?


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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Wed 08, 2020 8:51 pm 
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FuzzyDriver wrote:
devilsmist: Incoming RF? How does that get past the power supply? I actually saw the signal improve on my oscilloscope from when I started. The waveform lines were thick, indicating noise, but were thinner and more intense after I was done.

He said "RF off the incoming power lines", not "incoming RF". The 324 can couple its RF output onto the line cord, which then can radiate or conduct RF into the receiver under test. If you are trying to align a receiver, you want to be able to control the RF input level so you can reduce it below the AVC threshold. You do that using the attenuator on the signal generator. If there is also RF being coupled in from the power line, then you don't have proper control over the signal level fed to the receiver.

As for conducting RF in past the power supply in the receiver, there is usually capacitive coupling between the primary and secondary of the power transformer (most receiver power transformers don't have Faraday shields), the rectifier tube has some capacitance between cathode and plate, and the electrolytic filter capacitors have enough parasitic inductance that they don't filter RF. So now you've got RF riding on your B+.

FuzzyDriver wrote:
Dale H. Cook: Now YOUR reply is intriguing. There is a fundamental issue with service-grade equipment that makes it which? Impractical to upgrade or nearly impossible to upgrade? Your lab-grade signal generator is awesome looking.

Nearly impossible. The GR 805C has many more stages than your 324. There's no way you could fit all the parts you'd need on the 324's chassis, nor could you power them from the 324's power supply.

FuzzyDriver wrote:
But does it really take that level of equipment to get a cathode follower to not distort its input? Now you guys are going to get me back into that 324 instead of working on my other tube stuff!

You've missed absorbing Tom Bavis's post. The cathode follower has to be non-linear in order to modulate the RF with the audio. If you make it linear, you won't be able to modulate the output.

FuzzyDriver wrote:
You mentioned that I might not have the experience to work on lab equipment.

He said you might not have the "instrumentation and experience" required, presumably meaning "and/or". For example, in the quoted post you've already said you don't have a way to accurately measure RF output level to calibrate the output level VTVM in the GR 805C, and to verify the output of the calibrated attenuator.

FuzzyDriver wrote:
I hesitate to give my background in a post, but I also don't see anywhere in my profile where I can put it. Did I miss something? Shouldn't each of us be able to at least put something into our profile so other members can tell at a glance if they are replying to a newbie or a very experienced electronics technician? You have some info in your 'Occupation' field (BTW, interesting that you specify "instrumentation" rather than leaving your interest generic). Should I put all my years of experience there?

One's level of knowledge is generally obvious from one's posts.

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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Wed 08, 2020 9:33 pm 
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FuzzyDriver wrote:
There is a fundamental issue with service-grade equipment that makes it which? Impractical to upgrade or nearly impossible to upgrade?

Nearly impossible - service-grade equipment is designed and manufactured entirely differently than lab-grade equipment.

FuzzyDriver wrote:
But does it really take that level of equipment to get a cathode follower to not distort its input?

It depends upon how low a level of distortion is needed. The carrier distortion and noise in my 805-C is under 2%. The envelope distortion and noise is under 1%. I need that level of performance because I substitute the 805-C for the exciter in broadcast transmitters when working on their amplifier modules on the bench.

FuzzyDriver wrote:
(BTW, interesting that you specify "instrumentation" rather than leaving your interest generic)

I have owned, used, repaired and calibrated GR, HP, Tektronix, and other instruments for my work for more than 40 years.

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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Wed 08, 2020 10:32 pm 
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Thank for clarifying that. I did think he was talking about RF coming into the 324 rather than the 324's RF making its way out. Are you sure that's what those caps are for? I thought they are a primitive, quasi-safety setup since it originally had no earth ground - kinda like what you see in AA5's.

Re. Tom Bavis post, I didn't miss it. I'm just having trouble believing it and don't want to insult anyone. I already knew that if you are trying to get the sum and difference frequencies then that's what you need (like a superhetrodyne mixer putting out the IF (and ignoring the AF modulation, I must add) ). But that's not what we are trying to get here. We're trying to modulate the carrier - and keep the modulated signal, not the sum or difference frequency. It's not logical that you can't vary the amplitude of a sine-wave carrier, it has to be distorted or you can't vary it? But I can make a mistake so I did some internet research to see if my ET school memory had failed me and found a modulation demonstration project where the guy used one perfect sine wave oscillator to modulate another. He mixed them with an FET and showed the output waveform. His oscilloscope clearly shows the modulation taking place. The presence or absence of sum & difference frequencies were not mentioned (or relevant, IMO).

Quote:
...you've already said you don't have a way to accurately measure RF output level to calibrate the output level VTVM in the GR 805C, and to verify the output of the calibrated attenuator.

I think you have me mixed up with someone else there. I don't recall ever mentioning a VTVM or trying to measure the output of a calibrated attenuator.

Quote:
One's level of knowledge is generally obvious from one's posts.

Well...to some degree. I can tell that 'Retired Radio Man' is packed to the brim with practical experience and knows what he is talking about. On the other side, some guys are obviously newbies that I wouldn't trust to hold the right end of a soldering iron. But it takes a while to gauge people somewhere in the middle.

What would you say my level of electronics knowledge is? (just messing around for fun, you don't have to answer.)

Have a good one, and thanks again for the long reply, Steve - so many seem curt and dismissive!


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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Thu 09, 2020 12:29 am 
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FuzzyDriver wrote:
Thank for clarifying that. I did think he was talking about RF coming into the 324 rather than the 324's RF making its way out. Are you sure that's what those caps are for? I thought they are a primitive, quasi-safety setup since it originally had no earth ground - kinda like what you see in AA5's.

The line caps in receivers are to keep the RF on the power line out of the receiver. The line caps in a signal generator are to keep the RF from getting on the power line in the first place.

FuzzyDriver wrote:
Re. Tom Bavis post, I didn't miss it. I'm just having trouble believing it and don't want to insult anyone. I already knew that if you are trying to get the sum and difference frequencies then that's what you need (like a superhetrodyne mixer putting out the IF (and ignoring the AF modulation, I must add) ). But that's not what we are trying to get here. We're trying to modulate the carrier - and keep the modulated signal, not the sum or difference frequency. It's not logical that you can't vary the amplitude of a sine-wave carrier, it has to be distorted or you can't vary it? But I can make a mistake so I did some internet research to see if my ET school memory had failed me and found a modulation demonstration project where the guy used one perfect sine wave oscillator to modulate another. He mixed them with an FET and showed the output waveform. His oscilloscope clearly shows the modulation taking place. The presence or absence of sum & difference frequencies were not mentioned (or relevant, IMO).

AM modulation is mixing, and there are sum and difference frequencies present in an AM modulated signal.

You can modulate a sine-wave carrier and get a good low-distortion output waveform if you use something like a balanced modulator (i.e. something close to a perfect multiplier), or if you follow the modulator with one or more tuned circuits. But those are much more complicated circuits than the cathode-follower modulator in the 324.

If you want to play with RF, you might benefit from reading through an ARRL Handbook. A pre-1970 Handbook would be best if you mostly want to play with tubes, but the modern ones should do just as well for the basic theory.

FuzzyDriver wrote:
I think you have me mixed up with someone else there. I don't recall ever mentioning a VTVM or trying to measure the output of a calibrated attenuator.

When Dale wrote "likely would require instrumentation and experience that you may not have", the instrumentation I mentioned is some of what you would need to properly repair and calibrate a signal generator like Dale's GR 805-C. Look, he wasn't disparaging your expertise, he was just pointing out that you may not have the instrumentation and experience needed to restore a laboratory-grade signal generator.

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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Thu 09, 2020 2:24 am 
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stevebyan wrote:
Look, he wasn't disparaging your expertise, he was just pointing out that you may not have the instrumentation and experience needed to restore a laboratory-grade signal generator.

Steve is correct - I was not disparaging your expertise - after all, I once had significantly less electronics expertise than you do, I just started 60 years ago. I think it good that you are willing to try to improve your equipment, but I don't think that the work that it would take to improve that EICO would yield improvements that would justify the time and effort.

I prefer to start with something that will do what I need with the quality that I need. Sometimes that means buying an instrument on the cheap that needs some work and servicing it myself since I have the experience and instrumentation to do so. For example, for working on something like my 805-C some specialized instrumentation is required, such as a good RF voltmeter for measuring the output level, and a distortion analyzer with an RF detector for measuring envelope distortion. One of the next projects to go (back) onto the bench (it has already been through triage) is a Tek 1503 TDR (as Scotty said in the NextGen episode "Relics", "No bloody A, B, C or D"). The 1503 has a CRT in it, which I prefer to the LCD screens of the letter-suffix variations, which have not held up well. Fortunately the problem in my 1503 is a bad DC inverter which is fixable, and for my $25 investment and some hours on the bench I will have a solid TDR.

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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Thu 09, 2020 4:30 am 
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Quote:
Jim Mueller: Please elaborate. They're important for what? Something besides what devilsmist said?

As stevebyan said, they're for keeping the RF inside the generator except for what comes out the attenuator controlled output. Having the power cord act as an antenna is not good. These capacitors would be better as ceramic types (lower inductance) than film types. My Precision E-200-C, also a service grade generator but a step up in quality, has a 2 stage LC filter in a shielded box for this purpose.

Quote:
Re. Tom Bavis post, I didn't miss it. I'm just having trouble believing it and don't want to insult anyone. I already knew that if you are trying to get the sum and difference frequencies then that's what you need (like a superhetrodyne mixer putting out the IF (and ignoring the AF modulation, I must add) ). But that's not what we are trying to get here. We're trying to modulate the carrier - and keep the modulated signal, not the sum or difference frequency. It's not logical that you can't vary the amplitude of a sine-wave carrier, it has to be distorted or you can't vary it? But I can make a mistake so I did some internet research to see if my ET school memory had failed me and found a modulation demonstration project where the guy used one perfect sine wave oscillator to modulate another. He mixed them with an FET and showed the output waveform. His oscilloscope clearly shows the modulation taking place. The presence or absence of sum & difference frequencies were not mentioned (or relevant, IMO).

That is not correct. You are absolutely trying to get the sum and difference frequencies. Those are the sidebands of the AM signal. If you remove them with a very selective filter, you no longer have modulation, only the unmodulated carrier. It sounds like you need to do some studying about RF and modulation. BTW, FETs can be operated in linear or nonlinear modes so if he got modulation on the output, he was using a nonlinear mode.

Quote:
What would you say my level of electronics knowledge is?

Your posts make it sound like you have experience with low frequency stuff. Single point grounding works well for audio but is a disaster for RF. The long leads invite oscillation at both the signal frequency and at other, unrelated frequencies (called parasitic oscillation). You didn't mention connecting the shield of shielded cables at only one end. That is another trick that frequently works well for audio but not for RF.

Now that I've guessed at your background I probably should tell you mine. It was mostly low-level analog design but for many years I was the only EE at my company so I also did digital design (including ECL that requires twisted pair with a terminating resistor to go from one IC to the next), power distribution (including finding wire colors that would be simultaneously approved by every country in the world), and FCC and CE compliance which required low RF emissions up into the microwave region and immunity to ESD, both of which required solid grounding of EVERYTHING. Another thing that frequently came up was finding replacements for parts that were no longer available; sometimes a drop-in substitute was available, sometimes it required a re-design. I also got to approve or reject design changes proposed by others. One that was always rejected was to change the length of a cable from 9'8" to 10', a difference of 4". It was rejected because it would require an additional, expensive, test for CE approval.

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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Thu 09, 2020 5:45 am 
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The people here all seem to have very different backgrounds in electronics.

Quote:
...the work that it would take to improve that EICO would yield improvements that would justify the time and effort.

Dale: OK, that is a reasonable statement and I probably should take it to heart and leave my 324 as-is. We used a TDR on my first boat to troubleshoot one of the power instruments (don't remember which range). We had them at the nuclear power plant I worked at, too, but I don't recall needing to use it there. Do you use a TDR much?

Jim: You have a fascinating background. Similar to mine in the level of detail requirements (but different details and source requirements).

I have been into electronics since I was 10; 52 years ago. At 13 I got my novice license (WN9KQA). Hammarlund HQ-110A and EICO Model 720 bought with paper route money. Made my own antennas, CPO, and keyer. I worked for a TV repairman for about 5 years. I joined the Navy, ET-Comm, then nuke school, Reactor Operator on submarines. They sent me to ETMS school on Ford Island. This is the Navy's toughest electronics troubleshooting and soldering program. The soldering part is a copy of the program NASA uses to train people to solder on spacecraft electronics. After I got out of the Navy (9 years), I started a combination RCA & Zenith franchise store. I was the only repairman. Did OK, but a headhunter called and hooked me up as a journeyman instrumentation and control technician at a nuclear power plant, so I closed the store. Everything has to be done exactly right in the nuclear I&C field, but there is little RF.

Quote:
Your posts make it sound like you have experience with low frequency stuff. Single point grounding works well for audio but is a disaster for RF. The long leads invite oscillation at both the signal frequency and at other, unrelated frequencies (called parasitic oscillation). You didn't mention connecting the shield of shielded cables at only one end. That is another trick that frequently works well for audio but not for RF.

My recent experience is in audio work (so you are kinda right); it's been over 30 years since I worked on RF. I obviously need to get up to speed on RF design principles. Gonna pore over my '86 ARRL handbook and other old books I have. Thanks!


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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Thu 09, 2020 11:09 am 
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FuzzyDriver wrote:
The people here all seem to have very different backgrounds __ ______

I took the liberty of deleting a couple of words from your statement......
We're all over the place----many of us (even with college degrees) could not design our way out of a wet paper bag. The most common shared attribute is probably practical experience.
Very early in my career, I decided that a camera system going out on a space mission needed automatic exposure, and I started designing it. It only took a few days for the relevant manager to inform me that my brilliant idea was not going to happen. There was no appeal possible, for the simple reason that the feature was not required for the success of the mission. By the time I retired, I had become one of the curmudgeons that enforced a popular NASA mantra: "Better is the mortal enemy of good enough".
More than once, I was the "bad guy" that walked into room with several engineers debating how to design something. Asking them what problem they were trying to solve--and getting no credible answer--it was my job to tell them to stop.

This mind-set is hardly unique to NASA--minimalist design is enforced in many different situations.

When you decided that the output waveform needed to be "cleaner", you got a very low level of "polite dissent". A similar endeavor in the NASA environment could have gotten you reassigned or even fired.
My harshest experience in this regard: In a monthly management report, the lead optical engineer wrote in the "problems" section that the design was not yet optimized. He already was known as a "cannonball polisher", and--for the project manager---this was the last straw. The engineer was removed from the project the next day.

What's more important than the diversity of our backgrounds is that most of us are nice people who mostly just try to help others.

The bottom line: Never stop having ideas.....and keep in mind that the people making critical comments have likely done the same kind of thing themselves.

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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Thu 09, 2020 3:35 pm 
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FuzzyDriver wrote:
We used a TDR on my first boat to troubleshoot one of the power instruments (don't remember which range).

Do you mean a boat as in a submarine? I can't think of any other type of boat that would have cabling long enough or critical enough to need a time domain reflectometer.

EDIT: I see from farther down in your post that you did indeed serve on a sub.

FuzzyDriver wrote:
Do you use a TDR much?

Not much nowadays as I am mostly retired, serving as contract engineer at only a few radio stations. I also serve as backup engineer for a couple of cluster engineers, and sometimes get called in when a young engineer gets out of his depth with a problem. I need a TDR to locate cable faults, most often in FM transmission lines. When you have hundreds of feet of coax at an FM installation you need to be able to tell the tower crew at what elevation they need to look for a fault in the line. It also helps if they know if they are looking for a short or an open. The TDR is one instrument that I use for diagnosing the cause of a high reflected power reading on an FM transmitter. The other is a General Radio Type 1602-AB UHF Admittance Meter, used with a Type 1216-A Unit I-F Amplifier plus appropriate Unit Oscillators, Unit Power Supplies, detector, tees, and other GR Type 874 components. That system allows me to measure impedances in the system, and can even allow me to measure the antenna input impedance from the ground.

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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Fri 10, 2020 6:55 am 
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Mark: May I split hairs a little? I understand and agree with your comments and like the 'Better is the mortal enemy of good enough' adage. If the design meets all the requirements then the design is done (and, therefore, I should leave my 324 alone). The less added extra design elements, the fewer things there are that can go wrong, so in that respect 'good-enough' is better than better (yikes that verbiage is awkward). But what about the actual production of the equipment? Just building on my comment about the soldering part of the Navy ETMS school, do you allow people with hobby-level, no-formal-schooling soldering skills to do 'good enough' soldering work? In ETMS school, we studied how to get PCB fillets perfect. Out we went to practice. I could see nothing wrong with one of mine under a magnifying glass; it seemed picture-perfect. I brought it to the teacher for inspection. He studied it with a jewelers loupe for a good minute and then asked me if I had smeared a booger on it. Obviously they were shoving perfection down our throats - there was nothing wrong with my joint and the re-do was no better than the first 'booger-contaminated' one, though he passed it the second time. Good enough wasn't good enough.

Dale: Obviously you need your TDR a lot more than we did. You have longer cables to check and more opportunity for a fault to develop. The one time I actually used one (I'm talking over 35 years ago) we found a funny return (not a full short or an open) somewhere between the NI's and the detector and had the entire cable replaced. There's no splicing those things. You have some pretty sophisticated equipment; that's the first I ever heard of an 'Admittance Meter'.


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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Fri 10, 2020 1:27 pm 
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FuzzyDriver wrote:
... that's the first I ever heard of an 'Admittance Meter'.

I sometimes need to measure impedances at radio frequencies. Before the advent of the network analyzer the standard instruments for measuring impedances up to 60 MHz were the General Radio 916/1606 series of bridges, which are adaptations of the Schering bridge circuit. I own and use a 1606-A. A VHF variant, the 1601-A, measured at frequencies from 10 to 165 MHz. At higher frequencies lumped-parameter bridge elements become impractical, so the 1602 series of admittance meters use coaxial line elements, and cover 40 MHz to 1.5 gHz. I own and use a 1602-AB. Because of the design it measures admittances, which are easily converted to impedance readings.

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Last edited by Dale H. Cook on Apr Fri 10, 2020 1:56 pm, edited 1 time in total.

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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Fri 10, 2020 1:51 pm 
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Stopping when the design is "good enough" typically avoids more parts being added, which increases risk. It also means that more time is available for test. (Another mantra: Get to the first full-up system test as soon as possible)

Soldering:
NASA is notorious for its soldering rules.....and for a variety of other standards. To be sure, this is expensive. But it also has a major benefit: When a subassembly gets into test, the team does not get derailed looking for workmanship problems.
When trying to deliver a complex widget on schedule, the "solder police" were seldom an issue. Engineers that wanted to make it "better" were often the biggest issue.

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 Post subject: Re: EICO Model 324 RF Output Waveform
PostPosted: Apr Sun 12, 2020 3:26 am 
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Retired Radio Man wrote:
Of course manufacturing costs mattered, they always do. If you can't sell it you don't make money. The design EICO came up is simple an d works well for the intended use. Take a look at the schematic for an HP-606 sometime. That's a wideband generator that puts out clean waveforms but it wasn't aimed at hobbyists, hams, and service shops and it cost a lot more than $26.95.

As for mounting things on the tube socket, that keeps the leads short and that's what you want unless you like stray inductance and capacitance.

RRM


I have an Eico 315 and an HP-606. There certainly is a world of difference between them when both are working right. At the moment my Eico is working and my HP is not. When you look at their schematics you can also see that there is a world of difference between the two when they are not working and you need to fix them! The HP is a monster to fix but I hope to get it working some day because then it will be an entirely different monster. Mine did at least include the long, long hex key that so many seem to be missing.

I am bothered by the Eico waveforms too and I have looked at fixing them. Surely it is possible to do so and you should be able to do that with a lot less tubes than HP used, as long as you are aiming for better performance, not HP level performance. But is it worth it? I thought about it and decided to get the HP even though the HP needs work. If the Eico is working as it was designed to work it will do the jobs it was built to do. With all its warts I have found it very useful in diagnosing a couple of 1920's radios and I am sure it is entirely adequate for all the other radios I have waiting their turns. If you want something better then you are better off just buying a better generator.

If what you want is a project that might consume a lot of effort without much to show for it then I suppose that improving an Eico is a worthwhile project. You might succeed and impress us all and inspire a lot of imitators. It certainly is possible, I just don't know how painful it would be. Eicos have been used for other projects. Some have converted them to Part 15 TX duty. Some have converted them to regenerative RX duty. I might do the latter with mine, or I might just sell it because I now have a Siglent function generator that can do the same work it can do until I get that HP fixed....


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