# Traynor Guitarmate Low Output Power and Oscillations



## ook ook (Jun 3, 2021)

Hi all,

I've been working on a Traynor YGM-1 for the past little while which has been having issues. I finally got around to getting an 8 ohm dummy load and putting a signal through the amp and I don't like what I see.

Here is my maximum "clean" output:









With about 24 V pk-pk, that's roughly 8.5 V RMS which only gives me about 9 watts output.

This is the amp cranked (volume and treble on full) without nfb, with a large input signal:









This is about 35 V pk-pk which gives me a maximum output running full tilt of 19 watts.
(Not really because the waveform is heavily distorted from your normal some wave. I could imagine this output power being closer to 25-30 watts if measured with a True RMS meter, which I don't currently have)

Here is the same situation as above, with nfb:









Again, only around 19-20 watts.


So clearly there is an issue. I also was noticing that at the rising edge of the waveform, there is oscillation when the treble is above ~50% and the volume is high enough. I then turned up the volume and treble all the way *with no signal going into the amp* and found this:









This is with the nfb disabled. This does not occur with the nfb loop switched into the circuit.

Any help and suggestions are appreciated. I'll be getting a schematic uploaded shortly.


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## ook ook (Jun 3, 2021)

Schematic here:


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## Paul Running (Apr 12, 2020)

Try to localize the source point of the oscillation by scoping points further back in the circuit...try mid-point and go from there. Once you know the point of origin, begin analysing the circuit area at fault; parasitic oscillation may be caused by quite a few factors however, until you localize the point of origin, you are speculating, some people have a knack for guessing right though.


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## Latole (Aug 11, 2020)

Schematic


https://el34world.com/charts/Schematics/files/Traynor/Traynor_guitarmaterev_ygm1.pdf


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## ook ook (Jun 3, 2021)

Paul Running said:


> Try to localize the source point of the oscillation by scoping points further back in the circuit...try mid-point and go from there. Once you know the point of origin, begin analysing the circuit area at fault; parasitic oscillation may be caused by quite a few factors however, until you localize the point of origin, you are speculating, some people have a knack for guessing right though.


Yeah, that's the plan. Just trying to see if anyone has any particularly good guesses. I'm considering putting a 47pF cap across the PI plates like Traynor eventually did with the YGM-3



Latole said:


> Schematic
> 
> 
> https://el34world.com/charts/Schematics/files/Traynor/Traynor_guitarmaterev_ygm1.pdf


Thanks, but this schematic does not match my amp. It left the factory looking different from this schematic and it's been modified as well. My schematic above is accurate.


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## Latole (Aug 11, 2020)

ook ook said:


> Thanks, but this schematic does not match my amp. It left the factory looking different from this schematic and it's been modified as well. My schematic above is accurate.


You do a great job with this sketch,


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## dtsaudio (Apr 15, 2009)

Two things. What's with the two diodes connected to the standby switch? Is this an attempt at a center tap?
Secondly, your amp is showing all the signs of a bad output transformer.


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## ook ook (Jun 3, 2021)

dtsaudio said:


> Two things. What's with the two diodes connected to the standby switch? Is this an attempt at a center tap?
> Secondly, your amp is showing all the signs of a bad output transformer.


Conversion to a full wave bridge rectifier due to the absence of a center tap.


Also, I just noticed that my OT is labelled "DBK9" which dates it to Nov. 1969, well into the YGM-3 era. Looks like my OT is not original as I had thought. Pot codes and original speaker date the amp to late 1967.


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## dtsaudio (Apr 15, 2009)

ook ook said:


> Conversion to a full wave bridge rectifier due to the absence of a center tap.


Yes, of course. The asymmetry of the diodes threw me. Should of looked closer.
Still think the OT is shot. What kind of signal swing is on the primary side (if your scope can handle the voltage).


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## ook ook (Jun 3, 2021)

I had a tech repurpose the ground switch as a nfb switch and it seems like the proximity of the signal wire to the power switch is causing/amplifying the problem.
EDIT: not looking to be the case, I might just be an idiot

I may try switching the ground switch and power switch so that the nfb wire isn't crossing over the power switch, or I'll just experiment with different nfb values and pick one, removing the nfb switch.

More probing and chopsticking to be done.



dtsaudio said:


> Yes, of course. The asymmetry of the diodes threw me. Should of looked closer.
> Still think the OT is shot. What kind of signal swing is on the primary side (if your scope can handle the voltage).


I'm not gonna measure the OT primary. Not sure my scope or the leads can handle the voltage. It's a pretty cheap unit. The probes are rated at 300V


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## ook ook (Jun 3, 2021)

Phase inverter plate (pin 6) with and without nfb:

















No issues here that I can see...


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## ook ook (Jun 3, 2021)

Okay, I've made some discoveries. The oscillation only occurs when probing across the dummy load or speaker directly, and not if I use the chassis as ground. While oscillation is present, moving the OT primary wires and the nfb wire away from the phase inverter input capacitor (0.02uF ceramic disk cap going into pin 7 of V4) drastically reduces the oscillation but does not eliminate it. At least I can't get the wires far enough to eliminate it.

Even while no oscillation is present, I'm still capping out at about 8-10 watts clean.

I took some DC measurements at the power tube grids (pin 2) with and without signal flowing. With no signal, they're basically 0 V, fluctuating around 10 mV. With signal however, (treble & vol on full) the grid on V5 sees -13 V and the grid on V6 sees -3 V with nfb enabled. Without nfb, it's roughly -18 V and -7 V. 

V5 plate: 
with nfb: 
no signal: 346 VDC signal: 360 VDC
without nfb:
no signal: 361 VDC signal: 365 VDC

V6: plate:
with nfb:
no signal: 385 VDC signal: 369 VDC
without nfb:
no signal: 385 VDC signal: 364 VDC


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## ook ook (Jun 3, 2021)

I have reason to believe this amp originally had a 20 watt OT (see Hammond 1750Z) rather than the 25 watt OT that is in there now (see Hammond 1750S). The 20w transformer has a primary impedance of approximately double the primary impedance of the 25w transformer. 10k vs 5.1k. 

Might be switching both transformers back to "stock"


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## ook ook (Jun 3, 2021)

Swapped the OT primary leads and confirmed that they were correct previously.

That positive feedback scared the shit out of me


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## ook ook (Jun 3, 2021)

New OT has not remedied my issues. I'm looking at around 11-12 watts clean output power. It wasn't the coupling caps coming from the PI either, I changed those for some .047 uF caps just to check. I have upped the grid stoppers to 15k as well.

The power tubes have different plate voltages even with different tube pairs and when swapping the two positions. 

Is it the tube socket itself? Am I gonna have to swap the tube socket?


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## ook ook (Jun 3, 2021)

Just jumpered in 220k resistors in parallel with the existing 220k grid leaks and the plate voltages have normalized so I'm gonna throw in some 100k resistors in their place as is found on the YGM-3


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## ook ook (Jun 3, 2021)

Update: I am going to tear my hair out


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## ook ook (Jun 3, 2021)

Just turned the amp on and my meter read over 900V b+ so I instantly turned it back off. 

Now I'm afraid to turn it on


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## ook ook (Jun 3, 2021)

Maybe my meter is out of whack because if I restart it when the voltage lowers to around 900V (starting around 1000-1050V when powered on), when it comes back on, it'll read ~350V instead


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## Paul Running (Apr 12, 2020)

ook ook said:


> Maybe my meter is out of whack because if I restart it when the voltage lowers to around 900V (starting around 1000-1050V when powered on), when it comes back on, it'll read ~350V instead


I've had a few cheap DVMs do that over the years; I still find the VTVMs the most reliable instrument for measuring HT voltages.


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## Jerome (Dec 4, 2015)

So , you have about 40 vdc difference on the output tube plates with no signal ? Seems wrong . They should be pretty much the same , within a few volts .
Primary impedance of the OT should be about 8K .


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## ook ook (Jun 3, 2021)

Paul Running said:


> I've had a few cheap DVMs do that over the years; I still find the VTVMs the most reliable instrument for measuring HT voltages.


Yes, it was definitely the meter. I borrowed one and it's showing proper voltages.


Jerome said:


> So , you have about 40 vdc difference on the output tube plates with no signal ? Seems wrong . They should be pretty much the same , within a few volts .
> Primary impedance of the OT should be about 8K .


The plates are now sitting at 359 and 362 at idle. The OT primary impedance is 10k, the old one was 5.1k.

I am still only measuring about 25 V pk-pk maximum clean output voltage into an 8 ohm dummy load. 

~10 watts


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## Paul Running (Apr 12, 2020)

What frequency are you feeding to the amp? Are you disappointed with 10W? In my experience, it will take more effort now to squeeze the remaining potential from those tubes. Try not to exceed max. ratings for any extended periods of time, unless you have a generous supply of EL84s; I usually save my pulls separately contained and use them for above max. ratings experiments.


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## ook ook (Jun 3, 2021)

Paul Running said:


> What frequency are you feeding to the amp? Are you disappointed with 10W? In my experience, it will take more effort now to squeeze the remaining potential from those tubes. Try not to exceed max. ratings for any extended periods of time, unless you have a generous supply of EL84s; I usually save my pulls separately contained and use them for above max. ratings experiments.


I've run tests with a 500hz signal and a 1khz signal, amplitudes between 0.1 V and 0.05 V. I am a little disappointed with 10 watts. I was expecting something closer to 20 watts.

Right now the plates are at around 360 V and the screens are at roughly 345 V. I initially had the screens closer to 320 V, but the 2.2k resistor I had in the power section was running too hot so I dropped it down to 1.5k. If I wanted to run the screens cooler, I'd need to bump up the power rating of the 2.2k to 5+ watts and I don't have any of those on hand.

With a 178.6 ohm cathode resistor in place and 12.2 V across it, the tubes are idling at <11.5 watts.


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## Jerome (Dec 4, 2015)

At the onset of power tube clipping , what voltage do you have at the power tube plates and screens ? Do you have new output tubes in the amp ? What does the signal look like at the power tube grids when the amp clips ?


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## Hammerhands (Dec 19, 2016)

ook ook said:


> Swapped the OT primary leads and confirmed that they were correct previously.
> 
> That positive feedback scared the shit out of me


This was a good idea. Isn't there some common error about the transformer polarity and speaker polarity too?


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## ook ook (Jun 3, 2021)

Jerome said:


> At the onset of power tube clipping , what voltage do you have at the power tube plates and screens ? Do you have new output tubes in the amp ? What does the signal look like at the power tube grids when the amp clips ?


You can see earlier in the thread, post #11, what the signal at the tube grids looked like. It looked the same as the signal coming from the PI plates. However, I have since made some adjustments to the output section and have not taken new measurements.

I now have new output tubes in the amp and the plate voltages are stable and roughly equal. It seems that the amp is killing tubes very quickly if the voltage mismatch was due to faulty tubes. The new tubes did not increase the clean headroom though. I still only saw ~10 watts clean when I put the new tubes in.

I'm currently without a meter since mine is giving unreliable readings, so I'm just gonna live with the amp as it is until I get around to getting a new one. That being said, I'm certainly open to hearing anyone's suggestions


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## Jerome (Dec 4, 2015)

You should be able to get 18 watts from a pair of push pull EL84's , if : The tubes are good , the output transformer has the correct primary Z , the output transformer can handle 18 watts without saturating , the tubes are biased properly , plate and screen voltages are good , power transformer can supply the needed high voltage current , about 150 ma. , phase inverter can supply the needed signal voltage to drive the EL84's to full power .
I have built amps with EL84 's , my faves . A pair gives me 18 watts , 2 pairs , 36 watts . About 390 vdc on the plates , and a few volts less on the screens . Fixed bias . Have ran them like that for years .


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## epis (Feb 25, 2012)

1,5k screen resistors are choking your output tubes.


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## dtsaudio (Apr 15, 2009)

Jerome said:


> What does the signal look like at the power tube grids when the amp clips ?


Good point. You might be running out of gas further upstream.


Hammerhands said:


> Isn't there some common error about the transformer polarity and speaker polarity too?


The common error is wiring the plate/screen (primary) connections to the wrong tubes. This reverses the phase of the signal, so with feedback connected it becomes positive feedback, and the amp oscillates like hell's breaking loose.
Reversing either the primary, or the secondary (where ground and feedback connect) will cure this.
Sorry for the derailment.


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## ook ook (Jun 3, 2021)

Jerome said:


> You should be able to get 18 watts from a pair of push pull EL84's , if : The tubes are good , the output transformer has the correct primary Z , the output transformer can handle 18 watts without saturating , the tubes are biased properly , plate and screen voltages are good , power transformer can supply the needed high voltage current , about 150 ma. , phase inverter can supply the needed signal voltage to drive the EL84's to full power .
> I have built amps with EL84 's , my faves . A pair gives me 18 watts , 2 pairs , 36 watts . About 390 vdc on the plates , and a few volts less on the screens . Fixed bias . Have ran them like that for years .


Tubes are good.
OT primary is 10k.
OT is rated for 20 watts
Cathode bias idling between 95-100% dissipation.
Plates are at about 360 and screens at around 340.
I'll need to go back and take signal measurements throughout the amp to see if I'm losing headroom anywhere in particular.



epis said:


> 1,5k screen resistors are choking your output tubes.


Maybe I'll put them back to the 470 ohm I had there previously at some point to see if you're right.


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## dtsaudio (Apr 15, 2009)

Another thought. You've mentioned your power supply at idle, but what's it measuring at full power. You might be running out of gas at continuous high power levels. Might even be pulling down too far at tne preamp stages.


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## ook ook (Jun 3, 2021)

dtsaudio said:


> Another thought. You've mentioned your power supply at idle, but what's it measuring at full power. You might be running out of gas at continuous high power levels. Might even be pulling down too far at tne preamp stages.


Aha, good thought. I'll for sure have a look at that when I get another meter


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## ook ook (Jun 3, 2021)

I've burned through 2 pairs of tubes in one month. It would be pretty unlikely that I was just unlucky. I'm not sure if it's just a case of modern el84 tubes not being up to the task and I really need to move to 7189s or there is some issue in the amp (would really not surprise me, but what the issue would be eludes me). I'm not exactly excited to buy 7189s, looking at the prices at thetubestore, especially if the amp will just kill them anyways


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## Paul Running (Apr 12, 2020)

If you move to 7189s, you should consider reducing the screen-voltage. Also make sure that pin 1 of the tube socket is not used as a solder tag...pin 1 and 2 are internally connected on a 7189a (the control-grid).


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## ook ook (Jun 3, 2021)

Paul Running said:


> If you move to 7189s, you should consider reducing the screen-voltage. Also make sure that pin 1 of the tube socket is not used as a solder tag...pin 1 and 2 are internally connected on a 7189a (the control-grid).
> 
> View attachment 429065


I suppose you would recommend that regardless? I have the screens around 340V at idle. I am not using pin 1 as anything, so nothing to worry about there.


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## Paul Running (Apr 12, 2020)

ook ook said:


> I suppose you would recommend that regardless?


Yes, I would. The screen-grid in virtually all audio tetrodes and pentodes are not designed to dissipate high currents...it's a small, flimsy wire that will physically distort when over-heated, not like a plate's structure and unlike the plate, you may not notice it red-lining.


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## ook ook (Jun 3, 2021)

Paul Running said:


> Yes, I would. The screen-grid in virtually all audio tetrodes and pentodes are not designed to dissipate high currents...it's a small, flimsy wire that will physically distort when over-heated, not like a plate's structure and unlike the plate, you may not notice it red-lining.


Alright, I'll see about shooting for 300V


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