Traynor YCV40 Low Output

[Ampere]

Hi, im repairing a Traynor that has multiple injuries. When I got it, it had a blown 6L6, main fuse and non working standby switch. I fixed the standby ( replaced the IRF830 fet, 4n35 optocoupler, 10v zener). More about that here: http://music-electronics-forum.com/t27151/ I also did the mods suggested here to protect the cirquit: http://traynoramps.com/downloads/servman/sm_ycv40.pdf
Now the standby works. Output is still quite low and distorts especially the low lotes.

My main concern is the output transformer. The DC resistance of the OT primary windings are 80 ohms and 130 ohms. That seems too big of a difference to me. What do you think? Connected the 8 ohm secondary to 3.15 volts AC (half the heater) and i got 2.5 volts from half the primary. Also the heater voltage dropped near zero. Continuety measurement was fine between the windings and the core. (no leakage) Just like to have your opininon before ordering a new transformer.

Also this is how a 900 Hz sine wave looks coming to the grids of the 6L6. (without output tubes).


There are two opamps (TL072) U1 and U2. They are getting 24 volts, but other then that I'm not sure how to tell if they are a 100 %.

Heres the schematic for this amp:TraynorYCV40.gif gif by naazrael | Photobucket

Bias current at 10 ohm cathode resistors of 6L6s is 42mA and plates have 410V. 12AX7s have plate voltages at the range of 160 to 240 or thereabouts.

-Niko

[g1]

What is the peak to peak voltage on that scope pic ? What is the max p-p you can get at the power tube grids when set up clean (master full)?

When you tested the OT and got 2.5V for half the primary, was it the same for both halves?

[Ampere]

I was using the 10x on the scope so it's 20 V a step. I get 80 V p-p before clipping.



The other primary measures 2V when the other one is 2.5V.

Also the heater voltage drops close to zero when connecting to the OT sec. The secondary measures 0.4 ohm DC resistance.

[Ampere]

I get a max clean signal of 16V peak-to-peak at the grid (pin 2) of the splitter

[g1]

I don't understand what you mean about the heater voltage and connecting to the OT secondary?

[Ampere]

I don't understand what you mean about the heater voltage and connecting to the OT secondary?

Its described on this page. How to test an output transformer:
Output Transformers

"Identify a secondary winding, 8 ohm tap if it's available, and hook up one and only one winding to either 1/2 of the 6.3VCT or to the variac. Make D^&%ED sure the variac is all the way down if you're using one of those. Make sure that no other leads are connected (or shorted together, or touching your screwdriver on your bench or... well, you get the idea). Check for safety load resistors on the output jacks or secondary windings. These can cause you to erroneously think it is bad. There must be no loads on any winding. Put your voltmeter on the winding, and the current meter to measure the AC current through it, hook up the 3.15 VAC source, and turn on the AC - not to the amp, but to the AC feeding the winding you're driving. The voltmeter should measure 3.15 (or close) volts AC, the light bulb (if used) should NOT be lit brightly, and nothing should be humming or smoking ;-). There should be only a little current going through the winding. If the voltage is lower than 3 volts, or you are pulling amps of current, then there is a load on the transformer, internally since you have disconnected all the leads, meaning that there is an internal short. (Which means that you ought to be sure that there is no other load on the transformer, because you're going to throw it away if it has an internal short - be sure you're right!)

If all is well, no smoke, flames, loud hum, poultergeists, or lightning, measure the voltage that now appears on the other windings. The voltages will be equal to the ratios of the voltages that will appear on these windings in normal operations. For the primaries of output tubes, this can be up to a couple of hundred volts, so don't think that you can relax your safety precautions - it can still kill you, even driven with 3VAC on the secondary of the output transformer. The half-primaries of the output transformer should have identical voltages on them. Secondaries should have multiples of the voltage you're putting on the tap you chose. If you used an 8 ohm tap, a 4 ohm tap will have about 2.3VAC on it, a 2 ohm tap will have 1.6VAC on it, and a 16 ohm tap will have about 4.5VAC on it."

[nickb]

Just a thought. The center tap of the heater winding is grounded as is one end of the OPT secondary. Is there any chance that you connected the 3.15V to the ground side of the OPT winding and so shorted it out?

[Ampere]

I had the OPT completely disconnected and even removed it from the chassis the second time it did the test. Also tested it with my signal generator which produces 3V p-p. Come to think of it I guess its safe to say the OPT is busted. Still I think there's something fishy happening at the phase inverter too. I think I'll check the plate resistors and coupling caps tomorrow. The PCB is a real PITA to work with.

[nickb]

I had the OPT completely disconnected and even removed it from the chassis the second time it did the test. Also tested it with my signal generator which produces 3V p-p. Come to think of it I guess its safe to say the OPT is busted. Still I think there's something fishy happening at the phase inverter too. I think I'll check the plate resistors and coupling caps tomorrow. The PCB is a real PITA to work with.

Agreed. Unusual though it is, it's toast.

Your average signal generator would have a hard time driving the OPT at 60Hz.

[J M Fahey]

google , make and use RG Keen's shorted transformer indicator.
Test it using the primaries (end to end or either end to CT ) because you have highest inductance there and indication is clearer.

I understand that for the earlier test you pulled the output transformer from the chassis, fan spread all wires so clearly none touched another and fed 3.15V from common to some speaker out tap, is that so?

If transformer behaved as a short, then it's dead.

As mentioned above, typical generators are meant to drive 600 ohms or higher, so not really suitable to drive a 4/8/16 ohms secondary, even worse at low frequencies, but you can connect it from CT (which becomes ground) and one plate end, and measure from CT to the other, received voltage at the other end should be roughly same as injected, and injected should be reasonably close to what's indicated at the generator (say 800mV to 1V at the 1V setting, not 40mV even if you get exact same at the other end).

[Ampere]

Thank you JM for the RG Keen test method. I tried it both ways as you described and no flash. But however, when connected the neon to the ends of the primary winding and 9V DC to the secondary winding (it has only one 8 ohm) It flashed. (no flash with either side to CT) But I guess that's what it would do even with shorts. I used a 9V battery with a neon-resistor assembly. Just to be really REALLY sure I'd like to see it flash on a working transformer, but don't have any at hand at the moment. Well I'll use my sunday for other projects and get back to you with updates later.

[J M Fahey]

No need for it to be a proper OT, it should also work on a regular PT, any kind you have lying around, say 220V/12V or similar.

Another test possible is to wire the full high impedance side in series with a filament light bulb (try 25W) , like in a light bulb limiter setup; a good OT will have high inductance, so high impedance at 50/60 Hz, the bulb ill be dim orange-red or darker; a bad primary will make it shine brighter.

Not *full* brightness even if shorted because in any case it has some DC resistance, from 50 to 100 ohms, while a PT primary typically has 5 to 10 ohms DCR but it's an indication.

To improve this test, with mains voltage applied to primary you can short (be careful, use insulated pliers to hold them, not bare hands) the speaker out secondary.
If bulb goes from very dim to quite brighter, you are shorting the transformer inductance, meaning it still has some; if no big chance, no inductance present (so shorted turns) , only primary DC resistance in the path which does not change no matter what you do to secondaries.

None of these tests is Lab quality, and require some operator interpretation, but are what we have available.

Another amp test, suggested by Enzo, was to replace OT with *any* OT you have around.

You are testing a 50W amp and have a 15W transformer available?
Not even spare but mounted on another, working amp?

Put them side by side, disconnect primaries from good ampand connect them to suspect one ... do you get at least good 10/15W? ... proof the old one is toast.

If we can't *measure* we can at least *compare* .

[Ampere]

I wrote a huge post and pressing quick replay, it said i hadn't signed in and go back etc.. and my post was gone.
..so
Gotta go walk the dogs so in short the main points were:

-output transformer broken (tested with a Soundcity 50 plus amp.)
-amp broken (tested with Soundcity transformer)
-Have new transformer.
-Get back to it next week, since now busy now with more urgent repairs..
Thank you for your help so far!

-Niko

[Ampere]

That did it!

Got it working now with the new transformer installed. When I tested it out with the output transformer from the Sound City amp, I must have gotten the plates hooked up the wrong way, out of phase. I guess.

Thank you guys for all the help with this. I learned new ways of checking an output transformer for defects. And also this Traynor YCV40 has some interesting circuit design that were new to me.