Tung Sol 6V6 Reissue consistent problem

[JoeM]

^^ Yes, verify the meter's reading correctly.

[Dave Curtis, dB AudioTech]

"It may be time to let your local amp expert sort it out for you."

Bring him your meter, too. He'll tell you if it's time to get a new one... ;o)

~DC~

[g1]

I measured my wall voltage with the meter to see if it's reliable and it seems so, it measured 210V (it's supposed to be 220V here in Belgium even a little higher)

It's the right wire, the blue one which is 230V, the wall voltage in Belgium.
PS : the PT is a MM Axiom FDR PRI 240

If you measure 210V coming out of the wall, then I don't think the blue wire (230V) is the right one .
A few possiblilities:
a) your meter could be bad. It was first suggested you check it several days ago, it doesn't seem you have verified it is good?
b) you have a wiring problem in your house and are getting low voltage at this outlet. Try measuring the mains AC elsewhere (maybe someone elses house). 210V seems quite low for 230V service.
c)the AC service is just poor in your country and 210V is as good as it gets. In this case you should switch over to the 220V tap at the PT primary.

[Wil]

Both resistor measured 50.2 ohm, which is good since they're supposed to be 100 ohm and are in parallel.



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Yesterday it was quite late and I made a mistake, I mistook the green and yellow and red and yellow which are both CT... Sorry for having wasted your time.

The tech told me to try the 220V instead of the 230V wire, no improvement.
I measured 217VAC in the cellar and in the bathroom... Didn't even try to go to a neighbour's house, we hate them all, haha! But I guess they hate us more than we do, and we never understood why, haha.

I'll visit my uncle tomorow with my amp to have some realiable measurements, then I'll be fixed.
About the hoffman board, it doesn't seem to hard to make (at least the board itself) I believe I can cut a board, make holes, put turrets and populate this board. So I guess I might do a bit of the labor to save some €€€.

[Dave Curtis, dB AudioTech]

If it's reading 20% low at 230v, then 6.3v minus 20% is about 5v...

[g1]

The tech told me to try the 220V instead of the 230V wire, no improvement.
I measured 217VAC in the cellar and in the bathroom

No improvement in what? We are interested in your heater voltages, the 6.3V (green) and the 5V (yellow). What do they measure when you used the 220V tap?
Did you leave the 220V tap connected or go back to the 230V tap?
Keep track of the actual AC voltage going into the amp, and what the heater voltage is with the 220V and 230V taps. Post your results.

[J M Fahey]

Wil, first of all thanks for posting the picture with all the notes attached, it shows you are comitted to repair this amp and makes it worth trying to help you.
Now, I'm still worried about your heater voltage measurements.
Having 215V on a nominally 220V tap does not explain the discrepance.
Not even if line voltage is supposed to be 230V !!!
It would mean either 2.27% or 8.7% , both acceptable.
And reduced to a smaller value by using the 220V tap.
That does not explain the 24% or more you are getting.
I have 2 theories which I would love to check.
1) I don't think the MM transformer was miswound (not *impossible* but .... ) but the guy soldering the wires might have had a brainfart (the new 120/60/100 19 y.o. foxy receptionist got into that room) and he picked the wrong colour pair (your 4.8VAC measurement looks suspiciously close to a healthy 5VAC winding) *or*
2) your multimeter is real poor . (sorry).
Most cheap digital multimeters , recognizable because they typically have only 2 VAC scales (usually 200V and 750V ) are not *real* AC meters but DC only ones (which is much simpler and cheaper) .... with a 1N4007 diode stuck in series with the regular DC metering system.
It works (sort of) to measure wall voltages, distinguish between, say, a 300V and a 12V secondary, but have *poor* precision which gets *much* worse precision when you want to measure low values.
In a 200V scale, 6.3V is already low, 3.15V even more.
Measuring a 9V battery to check accuracy is not enough; DC voltages are measured with quite good precision, the problem appears on AC.
These meters are meant for light home use, barely suitable at the bench.
Mind you, I have a couple and they have saved my *ss quite a few times, simply I don't trust them for AC.

[Tom Phillips]

...I'll visit my uncle tomorow with my amp to have some realiable measurements...

Please remember to bring your meter and compare your voltage readings to those taken with his meter. I look forward to knowing if we can trust that meter since we have been talking about it since post #32 in this thread.

The discussion is also starting to circle back on itself and repeat some of the same questions. When this happens it's a good time to re-read from the beginning to help keep on course.

If this amp was always a lemon it could turn out that it has one bad part, incorrect connection or other simple mistake that occurred during the original factory build. Whatever the case turns out to be you want to make sure that you do no further harm. Better to ask questions first than to let someone do shotgun replacement of parts.

I wonder why the original power transformer was replaced?

Have fun working with your Uncle.

Cheers,
Tom

[Wil]

I do agree with you. Cheap multimeter for AC measurements aren't that good. My uncle told me he could help me but not before next week.
But even if the PT tests good, I think I'll go PTP with a hoffman board. My amp is just too noisy and I want to restrat at the basics to learn even more.
I won't be able to say thanks enough, I realise I had the privilege to be helped by some, if not the best in the world regarding tube amps!
Thanks thanks thanks! I may come back to you when I'm sure that this PT is toasted (or not!).
In the meantime, any advice regarding the making, populating, etc... of a Hoffman Board ?
Have a nice day everyone!

[Wil]

Thanks Tom.
I just played the amp cranked with the Tung Sol for 30 minutes and then I measured 2mA for V7... My multimeter is a cheap one, but look somewhat reliable, but I don't really trust the VAC measurements I read. Yes the heater voltages are low, do you think the Power Transformer could be faulty ? Could that low heater voltage "kill" a tube ? Strange thing is that it always "kills" only one of the two...
Regarding the smoke, I don't think I can come from the PCB because, the smoke came from the underside, where there's only solders.
I also have a lot of white noise with the amp... Feels like I'm playing next to a waterfall...
I measured the voltage difference between pin 2 and 8 and only got 2.2VAC. I measured my wall voltage with the meter to see if it's reliable and it seems so, it measured 210V (it's supposed to be 220V here in Belgium even a little higher)

One year and a half later, I finally built an hoffman based ab763 deluxe reverb. The amp sounds really nice but that Tung Sol 6V6 problem is still there !
I'm already happy because the amp sounds amazing. But I really want to use those Tung Sol because they sound even better !
I put a brand new set of tung sol 6v6 and after 10min they were hot as hell ! I did not even try to play the amp.
What changes compared to the normally working JJ 6V6S :
-In the first 2 minutes, the current is fluctuating a lot;
-They heat a lot more.
I'll measure everything tonight but if you read the first post of this thread, voltages were fine.
So here are the solutions I imagined :
-Putting bigger screen grid resistors (1k5 5W)
-Change rectifier for 5u4
-Change the PT (not wanted).

Thanks for your help!

[Wil]

(can't edit my last post)
Well I re-read my first posts that date back to more than 1 year ago.

I found a bad solder on pin 3 of V5, didn't change anything but I didn't expect much from that repair.
Here's what I've just measured after letting the tubes warm up for 12 minutes :
JJ's :
V7=V8
Pin 2 : 2.2VAC
Pin 3 : 394V
Pin 4 : 394V
Pin 5 : -27V
Pin 7 : 2.2VAC
Pin 8 : ~0V
Biased at V7 19.5mA, V8 19.2mA.

Tung Sols:
Pin 2 : V7=V8=2.2VAC
Pin 3 : V7 392V, V8 391V
Pin 4 : V7 390V, V8 389V
Pin 5 : V7=V8=-30V
Pin 7=Pin2
Pin 8 : ~0V
Bias : V7 8.6mA, V8 25mA.

The first time I played the Tung Sols, they biased measurements were very close (so it's not a "lemon"). So it's defenetly my amp that kills those poor little tubes !

I believe the screen voltage is too high!
I will swap the grid stoppers with the screen resistors to have 1k5 at the screen and 470ohm for grid stoppers.

Identical plate and screen voltages seem bad to me.