Audio HUM from speaker suddenly appeared on D201

[capn357]

So I've been fiddling with this hand-wired D201 for weeks now trying to figure out what failed or what I broke to cause the manual receive (and transmit) to stop working. Tonight, within 10 minutes of finally finding and solving that problem (short on terminal block that effectively shorted pin 7 and pin 8 circuits on V302B), a loud audio hum suddenly appeared from the speaker.  It was as if someone [waiting to kill my joyful mood] flipped a switch.  This hum has the following characteristics:

1. The volume of the hum is constant and independent of the radio volume.
2. When powering on the unit, the hum does not appear until the tubes have warmed up  (more specifically, not until after the meter goes through its gyrations and just before the receive audio comes alive).
3. As I said before, this hum came out of nowhere and went from 0 to 60 (literally) instantaneously.

Any idea what would cause such a step function audio problem?

[bill]

Is the Radio still using all the original Components ? Such as the Electrolytic Capacitors ? Such as the 2 Multi-Section ones which are for the Power Supply ? Who's job are to Filter the 60 Hertz Alternating Current " Hum "...
Mainly, it is quite common for people to perform what is referred to as a 100,000 Mile Tune-Up by Nomad... Due to Old Age Components... I believe it involves replacing EVERY Electrolytic Capacitor in the Radio, as the Electrolyte Fluid within them dries out over time... Carbon Composition Resistors are said to not age well either and lose their Resistance, which will increase Voltages... One's eyes are a good piece of Test Equipment as one often sees some of these Carbon Comp. Resistors which appear to be much Darker in Color, often making it hard to read the Identifying Stripes that are Painted on them... Others appear to have "Blisters" on them, as if something is oozing out from within... Sure signs these Resistors are bad... One can Test these Resistors in Circuit, measuring as close to the Resistor Body as possible to determine if they are within Tolerance... One can refer to the Schematic and Test Circuit Voltages too to see if they are up to Specifications... It's Ying and Yang... Every Component is dependent on each other in order for the Radio to perform as it was Designed...
Yes, Owning and Operating these Radios can be expensive, especially if one is paying someone to do the work...
No Technician here, nor do I claim to be... Just a Hobbyist Tinkerer... Just echoing the Words of others when it comes to Vintage Electronics in general...
The Radio is full of Components never designed to last this long... To gain reliability, a Restoration is in order... It is quite common that an initial failure can cause other failures within the Circuit, that is referred to a Domino Effect, one thing fails then another then another...
Performing a 100,000 Mile Tune-Up eliminates a multitude of well-known Problematic Components prone to failure... Failure due to Old Age...

[Sandbagger]

Mar 20, 2017 23:10:36 GMT -5 capn357 said:

So I've been fiddling with this hand-wired D201 for weeks now trying to figure out what failed or what I broke to cause the manual receive (and transmit) to stop working. Tonight, within 10 minutes of finally finding and solving that problem (short on terminal block that effectively shorted pin 7 and pin 8 circuits on V302B), a loud audio hum suddenly appeared from the speaker.  It was as if someone [waiting to kill my joyful mood] flipped a switch.  This hum has the following characteristics:

1. The volume of the hum is constant and independent of the radio volume.
2. When powering on the unit, the hum does not appear until the tubes have warmed up  (more specifically, not until after the meter goes through its gyrations and just before the receive audio comes alive).
3. As I said before, this hum came out of nowhere and went from 0 to 60 (literally) instantaneously.

Any idea what would cause such a step function audio problem?

The most common culprit would be a failed filter cap(s). But I had an especially loud hum on one of my D201's caused by a bad tube, specifically the RF front end V300 6BQ7. I assumed it was a heater to cathode short, but whatever the case, it caused a major hum just like you described.

[2600]

So, the real miracle is that it worked as well as it did until the hum appeared.

The hum you are hearing is probably not 60 Hz, but 120 Hz. The full-wave bridge rectifier that feeds high voltage to the tubes produces two "peaks" to charge the filter caps for each 1/60th of a second 'cycle' of the 60 Hz AC power that gets rectified.
The hum you hear should be one octave above the sound you get from a halfway plugged-in electric-guitar cord.

The power-supply filter capacitors were not meant to last more than ten or fifteen years, let alone 40-plus. Good chance that this is a low-mileage radio, and that's why it took so long for this symptom to appear.

You can approach this problem two ways. First, you can check the capacitors and replace only the ones that are bad. Good chance that a close look at the underside of C5, the taller of the two aluminum "can" capacitors will reveal some light brown or black schmoo that has leaked out of it. And it can go completely bad without showing any external sign.

If you don't have a way to test capacitors, this will make it tougher to identify parts that look good but don't work any more.

And even if you test every one in the radio and replace just the ones that flunk, this will become a game that I call "Electronic Whack-a-Mole". One or two at a time the rest of the electrolytic caps that test good today will fail down the line. Not a matter of "if" but of "when".

The fact that the volume control won't affect what you hear points to C5. Doesn't mean that it's the only one that's failed. Textbook term for this is "supply ripple", because of how it looks on a 'scope screen. Ripple that's feeding into the audio circuits between the volume control and the speaker won't be affected by the volume control.

You can approach this any way you want. A commercial-quality repair would be to "re-cap" the radio as some folks call it. I call it the 100,000-mile tuneup, and replace every electrolytic cap in the radio, along with other wear-and-tear parts that we know from experience are the cause of common faults.

And if you want to make a 1974 car your daily driver, total up all the belts, hoses, seals, gaskets and bearings you would need to replace. The D201 will be cheaper to restore than a car. But 40-plus years takes its toll even if the mileage is low.

73

[bill]

Well, once again close, but no Cigar... LOL ... Yes, it shows the Bridged Rectifiers right there on the Schematic, BUT I wasn't smart enough to Add them into the Equation... Thanks Nomad for enlightening me, once again... I should have just stuck with just the Multi-Section Caps, rather than attempt to get too Technical... LOL

CE Manufacturing is making Multi-Section Can Capacitors once again and I believe are using Mallory's Tooling and Specifications from years prior...
www.cedist.com/products/capacitors?filters=Type%3DMulti-Section%20/%20Can%20Type
One can also use JJ Tesla Multi-Section Caps, but they require a Capacitor Clamp to mount them... At the time I restored my D201A, CE Caps weren't around that I was aware of anyway... At times, the "exact" replacement may not be available... It is OK to use Capacitors that have a higher Rating and also a higher Voltage Rating, BUT never lower... DO not shop for "New Old Stock" Capacitors as they are just that, Old... It is said that ELectrolytic Capacitors have an average Shelf-Life of 12 Years, so New Old Stock parts make no sense to buy...
One could also replace these Multi-Section with individual Capacitors too, as there is room enough to hide then under the Chassis Deck, maybe...
Some choose to "Re-Stuff" the Aluminum Cans with modern caps of the same rating that can be much smaller in physical size to fit in the Cans...
Here is a Website that I like to direct People to regarding Capacitors in general
www.antiqueradio.org/recap.htm
One has options as to how they wish to deal with the Multi-Section Can Caps... One can do some Comparison Shopping as far as Price...
The Multi-Section Can Caps can be had here, along with other Tram Parts and others' Parts, although probably more expensive
www.goldeneagleradios.com
Some people began putting together " Capacitor Kits " for certain Makes / Models of Radios, selling them on EBay and their own Websites too... These Kits may be more expensive than shopping, Item by Item, but if one gives themselves an hourly Rate to first compile a List and then Shop each individual Cap online it takes time and is somewhat frustrating... Whether one uses Mouser, DigiKey or wherever they normally shop... These' Kits" were not around when I did my Restorations of the 1st Tram D201A... When I restored my 2nd D201A, I purchased a couple of Capacitor Kits from a Fellow in Puerto Rico on EBay... He also had Resistor Kits...
Not positive " How Different " Electronically the VOX Radio is, so these Kits may not be an option for you...

Anyway... Good Luck with your Radio !!!

[capn357]

Mar 21, 2017 10:41:01 GMT -5 bill said:

Is the Radio still using all the original Components ? Such as the Electrolytic Capacitors ? Such as the 2 Multi-Section ones which are for the Power Supply ? Who's job are to Filter the 60 Hertz Alternating Current " Hum "...
Mainly, it is quite common for people to perform what is referred to as a 100,000 Mile Tune-Up by Nomad... Due to Old Age Components... I believe it involves replacing EVERY Electrolytic Capacitor in the Radio, as the Electrolyte Fluid within them dries out over time... Carbon Composition Resistors are said to not age well either and lose their Resistance, which will increase Voltages... One's eyes are a good piece of Test Equipment as one often sees some of these Carbon Comp. Resistors which appear to be much Darker in Color, often making it hard to read the Identifying Stripes that are Painted on them... Others appear to have "Blisters" on them, as if something is oozing out from within... Sure signs these Resistors are bad... One can Test these Resistors in Circuit, measuring as close to the Resistor Body as possible to determine if they are within Tolerance... One can refer to the Schematic and Test Circuit Voltages too to see if they are up to Specifications... It's Ying and Yang... Every Component is dependent on each other in order for the Radio to perform as it was Designed...
Yes, Owning and Operating these Radios can be expensive, especially if one is paying someone to do the work...
No Technician here, nor do I claim to be... Just a Hobbyist Tinkerer... Just echoing the Words of others when it comes to Vintage Electronics in general...
The Radio is full of Components never designed to last this long... To gain reliability, a Restoration is in order... It is quite common that an initial failure can cause other failures within the Circuit, that is referred to a Domino Effect, one thing fails then another then another...
Performing a 100,000 Mile Tune-Up eliminates a multitude of well-known Problematic Components prone to failure... Failure due to Old Age...

Of course you are right; I'm sure the radio could benefit from a wholesale cap and power resistor replacement.  I just thought because of the way this failed so suddenly that someone might have an idea of what might bring that on....plus I was aggravated that this happened so soon after I finally figured out that other issue I've been chasing for weeks.  I understand that those high voltage filter caps go south, but I would have thought that they typically gradually go south (from leakage) as opposed to the instantaneous failure that I experienced.

So based on Sandbagger's feedback, I first swapped out several of the tubes, but this didn't uncover anything or rectify the problem.  Then I figured I'd try out this brand new (new to me, actually I purchased a demo unit) LCR meter and check the filter caps.  I was skeptical of how well this would be able to check caps "in situ", but I have the benefit of having two other D201's available so I figured I could always check any reading that looked suspect against the other units to see if anything was out of the ordinary.

Lo and behold I found that one of the 10uF caps on C624 (one of the big silver canisters) showed 36K Ohms as opposed to ~10 uF.  I happened to have a 10uF 450 VDC cap on hand that I just alligator clipped in parallel to see if it would make a difference (I know it's not optimum, but I was just experimenting to see if it made any improvement).  Sure enough, the hum decreased significantly, although not entirely.  I guess I know now that a cap can fail instantaneously.

I'll probably eventually restore this particular unit although I haven't decided whether to have someone do it for me or tackle it myself.  If I do it myself, it'll take me so long that the first caps I replace will probably need replacing again by the time I replace the last ones

Thanks for the responses.

[capn357]

Mar 21, 2017 12:45:50 GMT -5 2600 said:

So, the real miracle is that it worked as well as it did until the hum appeared.

The hum you are hearing is probably not 60 Hz, but 120 Hz. The full-wave bridge rectifier that feeds high voltage to the tubes produces two "peaks" to charge the filter caps for each 1/60th of a second 'cycle' of the 60 Hz AC power that gets rectified.
The hum you hear should be one octave above the sound you get from a halfway plugged-in electric-guitar cord.

The power-supply filter capacitors were not meant to last more than ten or fifteen years, let alone 40-plus. Good chance that this is a low-mileage radio, and that's why it took so long for this symptom to appear.

You can approach this problem two ways. First, you can check the capacitors and replace only the ones that are bad. Good chance that a close look at the underside of C5, the taller of the two aluminum "can" capacitors will reveal some light brown or black schmoo that has leaked out of it. And it can go completely bad without showing any external sign.

If you don't have a way to test capacitors, this will make it tougher to identify parts that look good but don't work any more.

And even if you test every one in the radio and replace just the ones that flunk, this will become a game that I call "Electronic Whack-a-Mole". One or two at a time the rest of the electrolytic caps that test good today will fail down the line. Not a matter of "if" but of "when".

The fact that the volume control won't affect what you hear points to C5. Doesn't mean that it's the only one that's failed. Textbook term for this is "supply ripple", because of how it looks on a 'scope screen. Ripple that's feeding into the audio circuits between the volume control and the speaker won't be affected by the volume control.

You can approach this any way you want. A commercial-quality repair would be to "re-cap" the radio as some folks call it. I call it the 100,000-mile tuneup, and replace every electrolytic cap in the radio, along with other wear-and-tear parts that we know from experience are the cause of common faults.

And if you want to make a 1974 car your daily driver, total up all the belts, hoses, seals, gaskets and bearings you would need to replace. The D201 will be cheaper to restore than a car. But 40-plus years takes its toll even if the mileage is low.

73

Indeed it is likely 120 Hz as you say.  Certainly there is some amount of 120 Hz that is still making it through to the keyed audio because I can see that on the spectrum analyzer display.  It's a good ways down from the main audio, but it is there nonetheless.

I hope I'm not causing frustration with my constant questions and my "whack a mole" approach.  I've much appreciated the insight and there is no doubt that the advice has helped me successfully beat the moles down thus far however slow and inefficient I may be.

That notwithstanding, I might be interested in having a professional restore at least the hand-wired D201 that I recently acquired.  Please pardon my further ignorance, but I don't know who does this kind of restoration professionally.  Do you guys have any recommendations in this regard?  I'm in the Atlanta area if that makes any difference.

If

[Sandbagger]

Mar 21, 2017 17:15:24 GMT -5 capn357 said:

Mar 21, 2017 12:45:50 GMT -5 2600 said:

So, the real miracle is that it worked as well as it did until the hum appeared.

The hum you are hearing is probably not 60 Hz, but 120 Hz. The full-wave bridge rectifier that feeds high voltage to the tubes produces two "peaks" to charge the filter caps for each 1/60th of a second 'cycle' of the 60 Hz AC power that gets rectified.
The hum you hear should be one octave above the sound you get from a halfway plugged-in electric-guitar cord.

The power-supply filter capacitors were not meant to last more than ten or fifteen years, let alone 40-plus. Good chance that this is a low-mileage radio, and that's why it took so long for this symptom to appear.

You can approach this problem two ways. First, you can check the capacitors and replace only the ones that are bad. Good chance that a close look at the underside of C5, the taller of the two aluminum "can" capacitors will reveal some light brown or black schmoo that has leaked out of it. And it can go completely bad without showing any external sign.

If you don't have a way to test capacitors, this will make it tougher to identify parts that look good but don't work any more.

And even if you test every one in the radio and replace just the ones that flunk, this will become a game that I call "Electronic Whack-a-Mole". One or two at a time the rest of the electrolytic caps that test good today will fail down the line. Not a matter of "if" but of "when".

The fact that the volume control won't affect what you hear points to C5. Doesn't mean that it's the only one that's failed. Textbook term for this is "supply ripple", because of how it looks on a 'scope screen. Ripple that's feeding into the audio circuits between the volume control and the speaker won't be affected by the volume control.

You can approach this any way you want. A commercial-quality repair would be to "re-cap" the radio as some folks call it. I call it the 100,000-mile tuneup, and replace every electrolytic cap in the radio, along with other wear-and-tear parts that we know from experience are the cause of common faults.

And if you want to make a 1974 car your daily driver, total up all the belts, hoses, seals, gaskets and bearings you would need to replace. The D201 will be cheaper to restore than a car. But 40-plus years takes its toll even if the mileage is low.

73

Indeed it is likely 120 Hz as you say.  Certainly there is some amount of 120 Hz that is still making it through to the keyed audio because I can see that on the spectrum analyzer display.  It's a good ways down from the main audio, but it is there nonetheless.

I hope I'm not causing frustration with my constant questions and my "whack a mole" approach.  I've much appreciated the insight and there is no doubt that the advice has helped me successfully beat the moles down thus far however slow and inefficient I may be.

That notwithstanding, I might be interested in having a professional restore at least the hand-wired D201 that I recently acquired.  Please pardon my further ignorance, but I don't know who does this kind of restoration professionally.  Do you guys have any recommendations in this regard?  I'm in the Atlanta area if that makes any difference.

If

The Tram D201 does not age well. Due to the design of the power supply and the heat that is generated by all the power dropping resistors, parts tend to age less gracefully than they do in similarly aged radios like a Browning MK III for instance. You are basically playing Russian Roulette when you use the "Whack-A-Mole" approach to replacing parts. The only safe way to do it, is to do all the electrolytic caps and the carbon power resistors, and any other part that comes up out of tolerance.

As for who does this kind of work, The most common places that come up are Barkett, Tubes Plus (Fixr), and Nomad. It's not going to be cheap to have these guys do it, but it will be done correctly.

[bill]

Given my lack of knowledge, I like questions, as it helps me learn more... I try to figure out the problem(s) and SHOULD wait for the more knowledgeable to Answer and then compare mine to theirs, as at times I am wrong Just like previously by not adding the Bridge Rectifiers to determine the Frequency of the Hum... No big deal though as far as being corrected, as it is ALL part of Learning to me... Don't beat yourself to death about asking questions as you seem to have a good amount of knowledge enough to do the Restoration... It reads like you have the desire to become more involved as you invested in Test Equipment... You must find some pleasure in doing it, or you probably wouldn't have made it this far with the Radio... People here are good people possessing a lot of knowledge and helping others is the reason the Group exists...
Closer to your neck of the woods out of the 3 Technicians mentioned are, in no particular order, Nomad Radio in Louisville, Kentucky www.nomadradio.com Phone Number shown here www.facebook.com/pages/Nomad-Radio/163763540309430 and Greg Barkett in Trinity, Alabama www.goldeneagleradios.com as Alan is in Parker City, Indiana www.tubesplus.com ... In your search, you might find that some Techs might not offer, Ship-In, Ship-Out Service though as Shipping Companies can be brutal...
No offense to any Tech, but as was mentioned a Restoration is not going to be cheap... Not sure what the going Labor Rate is, but I've heard it can take 4-1/2 Hours more or less, plus Parts, plus Shipping both ways... One has to Pack the Radio carefully if Shipping is involved... Shipping in itself is not cheap and it comes with risk of Damage or worse...
One could always get on the Radio and ask other Operators where they have their work done too locally... One could also possibly find an Amateur Radio Operator Club nearby to visit on their Meeting Night and ask about any Tech who belongs... Just suggesting some options...

[capn357]

Mar 22, 2017 5:40:09 GMT -5 bill said:

Given my lack of knowledge, I like questions, as it helps me learn more... I try to figure out the problem(s) and SHOULD wait for the more knowledgeable to Answer and then compare mine to theirs, as at times I am wrong Just like previously by not adding the Bridge Rectifiers to determine the Frequency of the Hum... No big deal though as far as being corrected, as it is ALL part of Learning to me... Don't beat yourself to death about asking questions as you seem to have a good amount of knowledge enough to do the Restoration... It reads like you have the desire to become more involved as you invested in Test Equipment... You must find some pleasure in doing it, or you probably wouldn't have made it this far with the Radio... People here are good people possessing a lot of knowledge and helping others is the reason the Group exists...
Closer to your neck of the woods out of the 3 Technicians mentioned are, in no particular order, Nomad Radio in Louisville, Kentucky www.nomadradio.com Phone Number shown here www.facebook.com/pages/Nomad-Radio/163763540309430 and Greg Barkett in Trinity, Alabama www.goldeneagleradios.com as Alan is in Parker City, Indiana www.tubesplus.com ... In your search, you might find that some Techs might not offer, Ship-In, Ship-Out Service though as Shipping Companies can be brutal...
No offense to any Tech, but as was mentioned a Restoration is not going to be cheap... Not sure what the going Labor Rate is, but I've heard it can take 4-1/2 Hours more or less, plus Parts, plus Shipping both ways... One has to Pack the Radio carefully if Shipping is involved... Shipping in itself is not cheap and it comes with risk of Damage or worse...
One could always get on the Radio and ask other Operators where they have their work done too locally... One could also possibly find an Amateur Radio Operator Club nearby to visit on their Meeting Night and ask about any Tech who belongs... Just suggesting some options...

Thanks.  I've made some inquiries.

[BBB]

On topic video from Uncle Doug. Good basic stuff...

[Sandbagger]

Apr 12, 2017 9:24:39 GMT -5 BBB said:

On topic video from Uncle Doug. Good basic stuff...

Heater-Cathode connection was what was causing the hum in one of my Tram D201's. But it was the RF front end tube and not an audio tube, which made tracking it down that much more "interesting".....