Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Aug Sun 19, 2018 2:22 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 16 posts ] 
Author Message
 Post subject: Siltronix 1011D Repair
PostPosted: Jul Thu 27, 2017 2:05 am 
Member
User avatar

Joined: Jan Thu 06, 2011 6:32 pm
Posts: 284
Location: Bethpage, NY
Hi I tried two radio shops to repair my Siltronix 1011D, and have had no success. The issue is it receives spot on, but transmits only a carrier with no audio, if any weak and distorted. I realize these units were drifters, but for years it was working fine after a 30 min warmup, then it went off frequency for transmit only with just a strong carrier. Usual suspects were checked (tubes, caps, the mic itself) but no success. Anyone here may offer their talent and expertise to repair it? Of course I would pay postage both ways, and your repair cost. One guy even went through the alignment process in the manual and it didn't help.


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Jul Fri 28, 2017 11:29 am 
Member
User avatar

Joined: Nov Mon 02, 2009 7:01 am
Posts: 2885
Location: Lincoln City, OR
Greetings to snowlion and the Forum:

There must be someone closer to you than I am (I am on the Oregon coast) that can look at it for you. It sounds to me as though you have a problem with the balanced modulator. In the older Swan rigs, this was a beam-deflection tube. Since the Siltronix is solid state (as I recall) it is probably a diode ring. Look around that circuit if you have the test equipment.

Regards,

_________________
Jim T.
KB6GM


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Jul Fri 28, 2017 11:55 am 
Member
User avatar

Joined: Jun Sun 19, 2011 2:31 pm
Posts: 5541
When you get a carrier with no audio, is that in AM mode?

Jim, I looked at a schematic and the 1011D still uses a sheet beam tube for the balanced modulator but in this case a 6JH8 instead of a 7360; by the time the 1011 series came out this tube that was intended for the TV market was probably far cheaper than a 7360 and is one of the good substitutes for the now expensive 7360 although it does require some rewiring at the socket when subbing.

The 1011D has a pretty simple two stage 12AX7 mic amp so that should have been easy for the radio shop to troubleshoot using either a signal tracer or scope to see whether the audio is making it to the grid of the balanced modulator stage.

At this time I have too many other things going on to take on the repair and there should be someone on the east coast who can help. If someone takes it on, or you want to fix it yourself, there are several of us (like Jim) on the forum who have experience with a lot of vintage gear including Swan who created Siltronix as a fake separate company to avoid issuing CB oriented products under the Swan name. Since it is transmitting a carrier and if this is in AM mode it should then I would start by using a scope to trace the audio through the simple two stage 12AX7 mic amp and see if it is getting to the balanced modulator grid. If so then like Jim noted it is probably an issue with the balanced modulator. Also does it receive properly in SSB mode? If not the problem could be in the carrier oscillator stage which also acts as the BFO for receive.

Rodger WQ9E


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Jul Fri 28, 2017 10:47 pm 
Member
User avatar

Joined: Jan Sun 13, 2013 2:46 pm
Posts: 394
Location: Dallastown PA 17313
Snowlion, I sent you a pm with name & number of Mid Atlantic Radio Repair in Thurmont MD. I had him work on my Swan 700 CX.
Mike

_________________
" Volume control has gone to lunch "


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Aug Wed 02, 2017 12:02 am 
Member
User avatar

Joined: Jan Thu 06, 2011 6:32 pm
Posts: 284
Location: Bethpage, NY
Someone on another forum mentioned the Q3 modulation transistor may be at fault (2N706). Is it worth a try to see if it is causing the failing modulation, off frequency? Also, I noticed a carrier is being sent on SSB, that is not supposed to be, is it?


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Aug Wed 02, 2017 9:01 am 
Member
User avatar

Joined: Nov Mon 02, 2009 7:01 am
Posts: 2885
Location: Lincoln City, OR
Greetings to snowlion and the Forum:

In answer to your question:
Quote:
Also, I noticed a carrier is being sent on SSB, that is not supposed to be, is it?


SSB is actually a shortened abbreviation. The whole abbreviation is SSBSC which stands for Single Side Band Suppressed Carrier. Therefore, the carrier should be many dB down below the modulation peaks. I am too lazy to go look up the FCC rules right now, but I believe that carrier suppression for older radios such as your Siltronix had to be more than 30 dB, and for modern radios it is something like 42 dB.

This means that if your peak envelope power were 1000 watts, your carrier power would have to be less than 1 watt. Since you are not running 1000 watts out of that rig, almost any detectable carrier is too much. Since the carrier is suppressed in the balanced modulator, and since you have both a carrier suppression failure as well as loss of modulation, this combination led me to make my initial post of balanced modulator trouble.

Anything in that circuit area, including a "modulation transistor" has the potential to unbalance the balanced modulator as well as cause the loss of audio fault. It is worth a try; however, since your radio has a tube-type balanced modulator (as we are informed by Rodger, WQ9E.... thanks for the correction, Rodger), I would swap in a known good beam deflection tube (6JH8) as a first trouble-shooting try.

Regards,

_________________
Jim T.
KB6GM


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Aug Wed 02, 2017 4:03 pm 
Member
User avatar

Joined: Jun Sun 19, 2011 2:31 pm
Posts: 5541
I agree with Jim's point about first trying a new balanced modulator tube and like him I was a little surprised to see the radio still used a sheet beam tube as the balanced modulator although it is an excellent circuit, when working properly, but these tubes do tend to be somewhat short lived in providing the performance level needed as a balanced mixer without becoming microphonic or contributing hum.

Your Siltronix should have at or slightly over 40db of carrier suppression when it is aligned and working properly. The balanced modulator produces an output with most of the carrier suppressed and the crystal filter takes care of the rest with the 300 hz part of the audio usually sitting at around the -4 to -6 db point and the carrier is 300 hz further removed and will sit at the -10 to -15 point on the filter slope. Since your SSB receive is working OK it is likely that the carrier oscillator crystals (also used as the BFO for receive) and IF crystal filter are fine.

Rodger WQ9E


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Aug Fri 04, 2017 2:57 am 
Member
User avatar

Joined: Jan Thu 06, 2011 6:32 pm
Posts: 284
Location: Bethpage, NY
Mike, Peter said he does not work on Siltronix, so anyone else have a suggestion for a repair person?


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Jan Mon 22, 2018 7:40 pm 
Member
User avatar

Joined: Jan Thu 06, 2011 6:32 pm
Posts: 284
Location: Bethpage, NY
Anyone else suggest a repair center or someone willing to troubleshoot this rig? Seems on freq now but modulation audio is very weak and tinny even after changing tubes and using different mic. I was told you can’t use a power mic with this rig?


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Jan Tue 23, 2018 3:19 am 
Member
User avatar

Joined: Nov Mon 02, 2009 7:01 am
Posts: 2885
Location: Lincoln City, OR
Greetings to snowlion and the Forum:

I would take it on, but I am very far away from you and I am sort of booked up right now. I could be a last resort, however.

It seems to me that either Mark (pixellany) or Peter (Pbpix) of this Forum had a repair business for awhile. They are both highly competent and Peter is in NJ, while Mark is in Maryland.... both much closer to you. I don't recall which one had the business, but either one could probably solve your problem for you if they are still willing to take on new customers.

Alternatively, you could look online for Swan repair and see what you come up with.

However, I would suggest, if you have the necessary test equipment, that you go after the problem yourself. It could be a valuable learning experience for you. If you can find an Elmer in your area (perhaps through the local ham club) then that person might be willing to work with you on the problem.

Best of luck,

_________________
Jim T.
KB6GM


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Jan Tue 30, 2018 11:46 pm 
Member
User avatar

Joined: Jan Thu 06, 2011 6:32 pm
Posts: 284
Location: Bethpage, NY
Hi Jim T. I may take you up on that as I can't find ANYONE here in New York or New Jersey who will look at it.

I discovered something else, maybe you can direct me to a potential issue the xcvr has. When keying dead mike, on AM I of course get a carrier sent. switching to USB or LSB, I ALSO get a carrier! I thought carrier is only sent on AM, not sideband. Any idea where I should check before boxing it up to the west coast (UPS will love me!)

Also, I now have a power mic attached, while the audio is louder, still not as booming as the carrier itself is.


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Jan Wed 31, 2018 12:21 am 
Member

Joined: Jul Tue 21, 2009 1:38 pm
Posts: 826
Location: SW WA state
If you have an issue with that beam tube, you can generate carrier when in the SSB modes.


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Jan Wed 31, 2018 1:16 am 
Member
User avatar

Joined: Jan Thu 06, 2011 6:32 pm
Posts: 284
Location: Bethpage, NY
I will try another I have 3 and one I know is weak. Why would the amp tube send a carrier like in AM mode?


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Jan Wed 31, 2018 4:09 am 
Member
User avatar

Joined: Nov Mon 02, 2009 7:01 am
Posts: 2885
Location: Lincoln City, OR
Greetings to snowlion and the Forum:

If you have the schematic for your radio, it might help to look at it while trying to understand my explanation. The "beam deflection" or "sheet beam tube" is a very special sort of critter that is used to develop a double sideband suppressed carrier signal from an RF input to its control grid and an audio input to its deflection electrodes. It is effectively a balanced mixer.

When the mixer circuit is balanced, no energy appears at its output. When the circuit is deliberately unbalanced, then mixing products appear in the output. The mixing products are (in the case of our ham gear) the sum of the audio frequency and the RF frequency (upper sideband) and the difference between the RF frequency and the audio frequency (lower sideband.

If you look at the tube and its surrounding circuitry, you will observe that the tube has two conventional grids, two deflection elements and two conventional anodes (plates).

When an RF signal is applied to the first grid, an electron stream varying in intensity at the RF rate is focused and accelerated by the second grid (screen grid) and directed toward the gap between the two deflection elements. If the voltage on the two deflection elements is equal, the electron stream divides equally between the two anodes (plates). The two plates are connected to the two ends of a transformer winding with the B+ supply to the tube being fed from a center tap on this winding. Since the electron stream divides equally between the two plates of the tube, the resulting RF currents in the transformer winding are equal in amplitude and opposite in phase (polarity). The net result is no magnetic field to couple the signal to the secondary winding of the transformer (which is where the circuit output is taken) and thus, no output RF is present.

When a voltage is applied to one of the deflection elements, the signal no longer divides equally between the two plates in the tube. One of them has an increase in current and the other has a decrease in current. This results in a net unbalance in the currents in the transformer winding halves, which results in a magnetic field being present to couple energy to the transformer secondary and output occurs. If this voltage is DC, the circuit is steadily unbalanced and a steady signal at the output results. This is how the "tune" function works... it deliberately unbalances the balanced modulator so that a steady-state carrier is present so that the output stages can be tuned. There is also a "carrier balance" control that allows the DC potential on the deflection elements of the tube to be adjusted slightly to allow for manufacturing tolerances in the tube and component variations in the surrounding circuitry.

(Note that not all radios have this "tune" function; my Swan 350 does not. I must deliberately mis-adjust the front panel carrier balance control to get a carrier for tuning purposes. This is a mod that Swan did to preserve the output tubes.... using this technique, it is possible to limit the RF drive to the finals and so limit the off-resonance plate current to safe values. Earlier Swans simply unbalanced the modulator wholesale and one had to be very quick in tuning to resonance to preserve the final tubes.)

When the voltage applied to the tube deflection elements is an audio signal rather than a DC voltage, then the modulator is unbalanced in first one direction (plate A has the higher current) and then in the other direction (plate B has the higher current). This results in the above mentioned mixing products appearing in the output transformer secondary: an upper sideband signal and a lower sideband signal. One of these is removed by filtering and a single sideband suppressed carrier signal results.

In your case, since you have carrier appearing at all times, the balanced modulator is clearly unbalanced. In addition, you have very poor audio. This points to a problem in the deflection element circuitry. Other causes of unwanted carrier are an open winding on the output transformer, a defective beam deflection tube or an external magnetic field.

Since you note the audio problem, I would look first at the deflection element circuitry and the voltages associated with it.

I would be happy to look at it for you, but hopefully you can take a look for yourself. Measure the two deflection element voltages... these should be very nearly equal, and should be able to be shifted in polarity with respect to each other by the carrier balance control. Check for equal voltages on the tube plates.... if one is missing or they are very much different, you will have serious problems. Lastly, if you have a de-gaussing coil, de-gauss the tube shield (make sure there is one present) and the metal parts of the chassis near the tube (the whole chassis if it is steel).

Don't forget to use adequate safety precautions when making measurements on a live transmitter.... these radios contain lethal voltages. Also, do not neglect to have a suitable 50 ohm dummy load connected at all times when testing.

Good Luck,

_________________
Jim T.
KB6GM


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Feb Thu 01, 2018 4:49 am 
Member

Joined: Jul Tue 21, 2009 1:38 pm
Posts: 826
Location: SW WA state
Jim,

Thanks for taking the time to put together your most excellent explanation!
IIRC, my Swan 250 unbalances the 7360 to get AM output...

-Tom


Top
 Profile  
 
 Post subject: Re: Siltronix 1011D Repair
PostPosted: Feb Sat 03, 2018 6:48 am 
Member
User avatar

Joined: Nov Mon 02, 2009 7:01 am
Posts: 2885
Location: Lincoln City, OR
Greetings to the Forum:

For Frank (snowlion):

I posted a PM 2 or 3 days ago with my E-mail address; it is still in my "waiting pickup" folder. You might want to check your PM inbox.

Thanks everyone for letting me use the bandwidth for the above message.

Regards,

_________________
Jim T.
KB6GM


Top
 Profile  
 
Post New Topic Post Reply  [ 16 posts ]  Moderator: Sandy

All times are UTC [ DST ]


Who is online

Users browsing this forum: Frank Dresser and 5 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB