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 Post subject: Knight Kit Spanmaster model 83Y 258
PostPosted: Jun Sun 06, 2010 12:33 am 
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Joined: Dec Sat 22, 2007 7:12 am
Posts: 2463
Location: Austin, Texas
Dear Fellow Members-Just won a clean one on EBay. She has a 6BZ6 and a 6AW8A tube,along with a 50 mA selenium rectifier and power transformer. Any opinions on what type of silicon rectifier and voltage dropping resistors to use when replacing this selenium rectifier? Thanx for any info:)-Gearhead-PS-Here's the link to the PDF schematic:)

http://bama.edebris.com/manuals/knight/spn-mstr/


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 Post subject:
PostPosted: Jun Sun 06, 2010 4:02 am 
Member

Joined: May Tue 30, 2006 4:46 pm
Posts: 10186
Location: Santa Rosa, CA
A 1N4007 diode will replace most any selenium you will find in a radio.

Here's more info.

http://w3hwj.com/index_files/RBSelenium2.pdf

Rich


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 Post subject:
PostPosted: Jun Sun 06, 2010 6:38 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 20548
Location: Sandpoint, IDAHO 83864
That is a different tube lineup than what I thought it was in our e-mail correspondence. I actually would not be the slightest concerned with any series resistance with a modern silicon diode like the 1N4007 series with this set. The secondary winding of the power transformer will have enough impedance to do any current limiting, but I don't even see where that would be required here.

Don't go making a mountain out of a molehill and complicate things for yourself. Besides, who is saying the selenium rectifier is bad? Just changing it out because it is a selenium rectifier is not troubleshooting. It is simply a fix for a problem that does not even exist.


Why some people adopt an attitude that things must be changed without any good reason is beyond me. It simply is more work and money and makes the set less original. But if that is your choice to replace it, and you have not even got the set in your hands yet, I sure won't be taking my car to you for repairs!
Curt

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Curt, N7AH
(Connoisseur of the cold 807) CW forever!


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 Post subject:
PostPosted: Jun Mon 07, 2010 4:23 am 
Member

Joined: Dec Sun 14, 2008 3:33 pm
Posts: 1067
Location: Tokyo
Since you've joined the Span Master fraternity, let me make a few suggestions from my experience with them. But please keep in mind I'm no electronics tech or engineer, just a former ham.

The set is about 50 years old, so just go ahead and replace the PS electrolytics. I'd make the first one at least 250V, and keep it around 50 to 100uF. The second one, after the filter choke, can be much larger. I have a 800uF/250V in mine. Yes, it did make a difference over the 200uF I first tried there: less hum.

I used a 1N4007 bridge to replace the selenium rectifier, plus 0.01/1000V discs across each diode. I've read the bridge circuit is easier on the PS transformer than the half wave, and a new one won't be easy to find. I have to point out that I've got only 100VAC, not 120 here. I did try 120 through a step up transformer, but the radio seems to prefer the lower voltage. My heaters are at only 5.1V, but there isn't any problem.

Float the heaters. This works virtually as well as filtered DC in getting rid of hum. Twist the leads, keep them close to the chassis, put a small pot (about 200 ohms or so) across them, ground the wiper.

A fair amount of hum is induced in the audio output trans from the PS trans. I moved it father away, from the speaker frame to the cabinet side of the bracket that supports the speaker. The trans is mounted horizontally, the long side parallel with the bottom of the wood cabinet. This is a small project. I use low Z hi-fi phones, which connect through the secondary of this trans. If you've got 2000 ohm phones, all this may not be necessary. I also had to add a 0.1 cap across the output trans primary to cut hiss.

The on/off switch on the volume control was moved to the speaker/headphones switch on the rear of the chassis. I replaced that switch with a DPST slide switch. Inconvenient location but I didn't like the AC cord running right by the sensitive audio circuits to get to the front panel. I installed a headphone jack on the chassis rear that cuts out the speaker, so that headphone/speaker was no longer necessary.

I guess I am rather obsessive about preventing hum. But nothing ruins the regen experience like hum, so I think it's worth doing whatever is necessary to avoid it. I want my regens to sound battery powered.

I think you'll find you'll need a RF attenuator pot for most SW listening: without it, the tank will be overloaded and the Span Master will not oscillate smoothly. Even with short wire antennas. Any linear taper pot from about 1K up should work fine. You can connect it across the set's antenna and ground terminals, and connect the antenna itself to the pot wiper. Set it so that the Span Master goes into oscillation smoothly, which for me is usually about the half way point. Every regen should have a RF attenuator.

The Span Master uses a 6BZ6, but I've tried many different RF pentodes and they all work more or less the same: 6BA6, 6HR6, 6AK5, 6GM6, etc. Right now one particular 6CB6 works the best. The low noise 6GM6 doesn't work any better than any of the others in this circuit, and in fact, struggles to get into oscillation at the low end of some bands.

I think the Span Master was the best of that 1960 era of kit regens. I really enjoy using mine. Congratulations on your find.

Rob


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 Post subject:
PostPosted: Jun Mon 07, 2010 8:36 am 
New Member

Joined: Jun Mon 07, 2010 8:34 am
Posts: 3
More SPAM.
Curt


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 Post subject:
PostPosted: Jun Mon 07, 2010 5:33 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3476
Location: La Porte, IN, USA
The Span Master was the second or third Knight Kit I built, back in the late 50's. Many happy hours.
But when i discovered the sensitivity and selectivity of an old Superhet, the Span Master went on the shelf--for a few years.
Later, I discovered the set could be modified--ever so slightly-- and become a Regenerative Preselector covering all the bands!
Just take off the signal through a capacitor (maybe .01 or so) at the plate of the first tube, and feed it into a superhet's antenna input. I also subbed a choke for the first tube's plate load resistor, but it would probby work with the resistor.
The resulting preselector actually improves signal to noise ratio, by narrowing the RF selectivity.
I found this a really neat use for a great old regen set that got it off the shelf and into action pepping up the front end of a superhet.
And these simple mod's do nothing to hurt the set's performance as it was intended.

_________________
Apolitical and Agnostic Forever (Well, on the Forum, anyway)! -OZ


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 Post subject:
PostPosted: Jun Mon 07, 2010 8:14 pm 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 10186
Location: Santa Rosa, CA
Quote:
I used a 1N4007 bridge to replace the selenium rectifier, plus 0.01/1000V discs across each diode. I've read the bridge circuit is easier on the PS transformer than the half wave,


It's not so much an issue of being "easier on the PS transformer," rather that the full wave bridge yields 120 HZ ripple, which is easier to filter than the 60 HZ ripple of a half wave rectifier.

I am surprised that there would be a difference between 200 uF and 800 uF as the second filter cap. 200 uF should be more than enough.

Rich


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 Post subject:
PostPosted: Jun Tue 08, 2010 1:11 am 
Member

Joined: Dec Sun 14, 2008 3:33 pm
Posts: 1067
Location: Tokyo
I was also surprised. There was a tiny bit of remaining hum with the 200uF in place, not really anything to complain about, but I wanted it completely clean. I clipped in another 200uF and noticed it lowered the hum. Four 200uF caps got rid of it completely, so I installed one 800uF. But I use a good set of Sony stereo headphones, with excellent bass response.

BTW, the PS transformer is not quite as warm to the touch using the bridge compared to using a single 1N4007.

I also built a Span Master when I was kid. I too realized I could use it as a regenerative preselector with my entry level superhet, unfortunately about 45 years too late!

Rob


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 Post subject:
PostPosted: Jun Wed 09, 2010 1:57 am 
Member

Joined: Dec Sat 22, 2007 7:12 am
Posts: 2463
Location: Austin, Texas
Dear Shinkuukan and others -Thanx again for the replies! Since my favorite local electronics store went out of business, I have resorted to the local F*** Electronics, which has a limited selection of caps. I have 2 33 mF @ 250 VDC before and after the AC filter choke, a 10 mF @ 250 VDC for the 8 mF @ 150 VDC, a 10 mF @ 35 VDC for the 10 mF @ 25 VDC, and a 22mF @160 VDC for the 20 mF @ 25 VDC. Any opinions here? Trying to keep this baby as stock as possible. I do have some 2000 ohm Trimm headphones also. Any opinions on antenna length?:)-Gearhead-PS-My 1963 Ford Falcon is bone stock, Captain Curt, except for the engine block and valve cover. After painting them Ford Blue, I discovered why Ford painted them black-oil leaks show!;)


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 Post subject:
PostPosted: Jun Wed 09, 2010 8:46 am 
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User avatar

Joined: Apr Sun 04, 2010 3:55 am
Posts: 1871
gearhead222 wrote:
F*** Electronics

????


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 Post subject:
PostPosted: Jun Wed 09, 2010 4:41 pm 
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Joined: Jan Wed 02, 2008 8:12 pm
Posts: 217
Fry's?


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 Post subject:
PostPosted: Jun Thu 10, 2010 12:06 am 
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Joined: Dec Sun 14, 2008 3:33 pm
Posts: 1067
Location: Tokyo
The values are very close to the original design, so no problem. The Span Master used a combination unit for the PS caps and the audio output cathode bypass, and that will be hard to find a replacement for, so in any case, the radio won't be stock. Keep in mind electrolytics used to be large and expensive, and that affected the values which were chosen. Today they are small and cheap. I'd consider increasing the size of the second PS filter cap, and also the decoupling cap to the detector stage (that 8uF). No point in increasing the size of the audio cathode bypass caps: with a 4 inch speaker you not going to hear any bass anyway. The easiest way is to just try the values you have and see how it goes. You can always wire in more capacitance if necessary.

The manual says 50 to 100 feet for the antenna. That's OK for the BC band, but I think you'll find such a long antenna will overload the detector tank circuit on SW. If it does, the radio will fight going into regeneration, it may start screeching too, and you can expect hand capacitance effects. For SW, 10 to 15 feet is enough. Or you can put a linear taper pot (something from about 1k to 10k) across the antenna and ground terminals, connecting the antenna itself to the wiper. Then you can use any length wire by adjusting the pot (this is a control that nearly always appeared in handbooks from the 1930s). Unless you've got a perfect RF ground, don't bother grounding the set: it often does nothing or even creates problems sometimes.

Rob


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 Post subject:
PostPosted: Jun Thu 10, 2010 5:38 am 
Member

Joined: Dec Sat 22, 2007 7:12 am
Posts: 2463
Location: Austin, Texas
Domo arigato Shinkuukansan!:)-Gearhead


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 Post subject:
PostPosted: Jun Sat 12, 2010 12:24 am 
Member

Joined: Dec Sat 22, 2007 7:12 am
Posts: 2463
Location: Austin, Texas
Dear Shinkuukan and others-Replaced 3 of the main filter caps and got her running. Unfortunately, the band switch keeps cutting out unless I jiggle her. Is there any easy way to clean the contacts on this? It's a wierd plastic and metal unit with the contacts partially enclosed. Don't even know if I can take her apart! Thanx for any feedback!:)-Gearhead


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 Post subject:
PostPosted: Jun Sat 12, 2010 1:02 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 20548
Location: Sandpoint, IDAHO 83864
I would try spraying some cleaner inside it if possible after making sure the cleaning solvent will not attack the plastic. Usually a bunch of switching it back and forth will help, especially if it has not seen use in a long time.

Keep messing with it and if all fails, then you are in for a replacement switch.

Sorry I missed your telephone call. I was leaning up against the razor when you called. Got to look spiffy tomorrow as I am going to a small hamfest. Probably will spend my $4 to get in and come home empty handed, but at that particular hamfest, one can never tell.
Curt

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Curt, N7AH
(Connoisseur of the cold 807) CW forever!


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 Post subject:
PostPosted: Jun Sat 12, 2010 4:35 am 
Member

Joined: Dec Sat 22, 2007 7:12 am
Posts: 2463
Location: Austin, Texas
No worries Capt. Curt! After completing recapping her, I discovered a cold solder joint on the fine regen control, which completes the regen circuit! When I jiggled the main regen control, it would make and break this connection! Works great now! Woo-woo!:)-Gearhead-PS-The original Selenium rectifer works fine:)


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 Post subject:
PostPosted: Jun Sat 12, 2010 1:21 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 20548
Location: Sandpoint, IDAHO 83864
Good! Glad to see it fixed and up and running like it should. Yes, you got to be very careful with any radio that was built from a kit as bad solder connections are quite frequent and eyeballing all the connections often does not show anything out of the normal.
Curt

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Curt, N7AH
(Connoisseur of the cold 807) CW forever!


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 Post subject: Re: Knight Kit Spanmaster model 83Y 258
PostPosted: Sep Mon 01, 2014 5:11 am 
Member

Joined: Sep Sat 06, 2008 3:04 am
Posts: 241
Location: Benton City, WA
gearhead222 wrote:
She has a 6BZ6 and a 6AW8A tube,along with a 50 mA selenium rectifier and power transformer. Any opinions on what type of silicon rectifier and voltage dropping resistors to use when replacing this selenium rectifier? PS-Here's the link to the PDF schematic:

http://bama.edebris.com/manuals/knight/spn-mstr/

The Span Master was my first kit and first receiver. Not the best for apartment swl'ing but I still managed to get over 50 countries with it in about 1962. It sure pales in comparison to most superhets and other later receivers but it was all I could afford as a kid just starting high school! It does bring back memories though!

As far as the selenium rectifier, like others have said, don't replace it just because.

You mentioned that the band switch acted intermittent. Do not just squirt some contact cleaner on the contacts. The best thing is actually to just work the switch several times. If you have to, take some deoxit on a swab and clean the contacts but do not just squirt it with deoxit or contact cleaner as that tends to make the phenolic swell and ruin the switch if too much gets on the phenolic.


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 Post subject: Re: Knight Kit Spanmaster model 83Y 258
PostPosted: May Mon 08, 2017 2:23 am 
Member

Joined: Sep Tue 10, 2013 8:04 pm
Posts: 45
Can anyone supply or post photos of the main and bandspread dial papers for a span master? Mine were water damaged. Thanks!


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 Post subject: Re: Knight Kit Spanmaster model 83Y 258
PostPosted: Jun Thu 29, 2017 12:01 am 
New Member

Joined: Aug Thu 11, 2016 10:39 pm
Posts: 22
Are you still interested in copies of the stick on dial plates on the Span Master? I'd be happy to do it and share with the site.

I recently started looking at a Span Master I picked up at a Ham Fest 15-20 years ago and just wrapped up and put on the shelf until I had time to work with it. I had to get it since it was my first radio back around 1961, but mine went missing somewhere along the way.

The one I got weirdly looked brand new and the guy said he didn't know if it worked. Yeah right, that's lingo for it doesn't work. Now that I've dug into it I see the darn thing is brand new. The kit builder was an expert at not only cold solder joints but applying lots of solder to wires and having them shiny and bright. . .but amazingly isolated from the terminal by a layer of flux. It LOOKS like it assembled except for the issue of conductivity.

So they must have turned it on and it didn't work at all and they didn't have the resources to troubleshoot. I just happened to luck out that it was carefully stored and not damaged. And I only recently figured this out.

I'm offering to copy the dials because they are pristine and the copying and restoration of images is a business I have. So I have a pro digital copystand setup. Still it will be a challenge due to the reflective nature of the dial labels. I also remember that the dials on my original Span Master were actually touched by the clear disc attached to the knob and in some spots the printing was worn off. These seem to have absolutely no wear.

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Wayne Munn


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