Tung Sol 6V6 Reissue consistent problem

[Justin Thomas]

Wil,

If nothing seems burned, I guess that's okay. For that heater voltage, yes a bad tube could pull that down. Funny that the PT has been replaced already. Pull ALL the tubes out and check the heater voltages at the pins. It should read at least 6.3V, possibly as high as 7 - my Fenders put out about 7.2V unloaded. Put the preamp tubes back in one at a time. The voltage should go down a little tiny bit with each tube. If you find one that knocks it down a lot, that may be it. If none of the preamp tubes do it, put in a power tube. Still okay, put in the last one. Then try with the other set of power tubes. It may reveal a bad tube - intermittent short, other fault. It's a percentage thing - you're running about 30% below spec. Okay in some areas, not so much for heaters.

And do what Joe suggested, checking the sockets. Sometimes the last person in the amp leaves a bit of mess. Not intentional, but can be a problem.

Are you the original owner or did you buy this used? Do you know any of its history?

Justin

[Wil]

I bought it used. It was made in 1999 and modified by CMW amps. I emailed the previous owner several times for the troubles I was having with the amp, he clearly told me to f*ck off...
When all the tubes (except the rectifier tube) are removed, I measure 5.5VAC... still too low
So the PT might be defective ?
Could a bad preamp tube or low heater voltage "kill" one of the Tung Sol power tubes ?

(once again, thanks for your help, it's greatly appreciated!)

[JoeM]

What Mercury PT is in the amp? Have you verified it's correct for the line voltage in your country?

[Justin Thomas]

Wil,

Definitely verify that the PT is correct for your country, though I googled the shop who did the mods and they're Dutch, so... maybe they made a mistake. Having the heaters that low with all the tubes out is definitely wrong. The PT may not be bad, though. But some more research is needed.

And, any solder bridges or blobs anywhere? Something's either drawing too much current, not wired right, or something.

Justin

[Leo_Gnardo]

Wil wrote: < modified by CMW amps. I emailed the previous owner several times for the troubles I was having with the amp, he clearly told me to f*ck off...
When all the tubes (except the rectifier tube) are removed, I measure 5.5VAC... still too low
So the PT might be defective >

Previous owner is telling you in so many words, he sold you a "lemon." FWIW I have found some bad Mercury transformers despite their self-claimed superiority.

Low heater voltage will not allow tube cathodes to heat properly and will result in low bias current readings.

It would be revealing to remove the Mercury PT filament winding from the circuit and substitute 6.3 VAC from a known good transformer. If this results in an improvement then you will know you have to replace your PT with a competently made one.

Considering the long series of problems you have had with this amp I wish you best of luck putting it right.

[Wil]

It's the right wire, the blue one which is 230V, the wall voltage in Belgium.
Today I measured 5.9VAC accross the heater wires... I don't even try to understand how it can vary from one day to another anymore... haha.
A strange thing is that I measure (with only the rectifier in) 650VAC across the two red wires (that go to the rectifier socket). According to Mercury it should be 345V.
Also, I measured 4.2V instead of 5V accross the yellow wires (the rectifier heater). Nonetheless, with the tubes removed (except the rectifier) I measure approx. 450VDC after the rectifer which I think is about right.
So, the PT looks toasted doesn't it?

PS : the PT is a MM Axiom FDR PRI 240

[Wil]

Thanks for the answer Leo.
One question still remains :
What could have caused one of the Tung Sol reissue power tube to fail ? (only one of the two).
I emailed Mercury Magnetics. Their custom support is great, that's a good point!

I have a new trail :
The center tap wire. I read it could lower the voltage of the heater filament. Should I remove and insulate it ? (but it features on the original schematic...)

I rely on this schematic :
http://ampwares.com/schematics/65_Deluxe_Reverb_RI.pdf
It shows, if I'm right, that the heater filament center tap is wired but also has what I just discovered, a "pseudo" or "virtual" center tap.
(please don't throw stones at me if I'm wrong haha!)

[Leo_Gnardo]

Wil wrote
<What could have caused one of the Tung Sol reissue power tube to fail ? (only one of the two).
I emailed Mercury Magnetics. Their custom support is great, that's a good point!

I have a new trail :
The center tap wire. I read it could lower the voltage of the heater filament. Should I remove and insulate it ? (but it features on the original schematic...)>

TungSol 6V6 as far as I can tell are EH (Sovtek) with different logo and higher price. In my experience they do not hold up in 450V B+ amps. I've had much better luck with JJ 6V6. I would not "blame the amp" for TS 6V6 failures. If you've had bad luck with TS 6V6 in your amp, common sense should tell you to avoid them.

Where did you read disinformation about center tap of the filament winding? There's a lot of bad information on the internet. Stick with MEF, the best and brightest techs in the world are trying to help you out here. (Joe, Tom, Juan, JMAF, Enzo & sorry if I left anyone out, you're all good, mostly... Day comes that Wil gets his DRRI sorted out properly there won't have enough champagne to go around.)

650V across the two red wires = 325-0-325 just a little under spec. Not much to worry about. 450V B+ is in the normal range.

If you disconnect CT on the 6.3V winding all you will get is a lot of hum.

Get back on the right trail Wil. Your PT is very suspicious. There may be other problems with your amp. Who knows what that mod shop did, and all the other attempts you have made to repair it since then.

Again, substitute 6.3 VCT from a known good transformer. If this gets your amp starting to work right, you know you have to replace your present PT.

[Wil]

Is there any way to check if a transformer is "healthy" ?
[QUOTE]Hi Wil

I mostly did/do use so called post pi mastervolumes in such amps so you have to re-install the bias-splitters. I also did install grid- and screengridstoppers on the tubesockets if I'm not mistaken.
If the installed MV is on 10 the circuit is like stock [QUOTE\]
Here's exactly what he wrote me back. No time to waste on the PPIMV conversion, the circuit is now exactly like stock (I really didn't like it).
My amp is noisy if it helps. A lot of white noise. Do you think a disconnected center tap could do that ? I noticed the noise what really getting worse when raising the volume, treble and/or disconnecting the NF wire. And these are things I have to do in order to have a some clarity.

I'm leaning toward putting an hoffman board from scratch in that amp... I bought the amp more than 8 month ago and never could make it work as I want it to. I'm quite demanding, but I do know how a Deluxe sounds and this one just doesn't.

Wow... Champagne might be a little pricey then! What about some of the best belgian beers, haha ?

[Justin Thomas]

Hey Wil,

That certainly adds something to the mix... The fact that BOTH of your heater windings are low (5V & 6V) without tubes in is very suspicious. Do what Leo said and check using another good transformer. If that doesn't help, try out R.G. Keen's transformer test page:

Power Transformer

It's pretty comprehensive in finding stuff you can eliminate yourself. The whole website is great for general debugging.

Hard to tell what other mods have been done to this amp over the course of its life. But let's get that PT sorted out. I saw the price of it - holy cow! And I live in he States...

Justin

[Leo_Gnardo]

Thanks for your support Justin. Once it is proven that Wil's PT is dodgy, I'm sure a replacement PT can be found in Europe for a fraction of Mercury's price.

In one of Wil's posts he mentioned there are BOTH heater center tap to ground AND "balancing resistors". Both methods are not needed. I suspect there may be something amiss with the resistors

Wil - have you tried running the amp with the filament "balancing" resistors removed? Before warming up the amp check for filament circuit continuity to ground with your ohm meter. A reading near zero ohms from filament 6.3 VAC line to ground would be right if the center tap is indeed connected to ground. I had a thought that if the value of one or both resistors isn't what it's supposed to be - and it's a lot less - that might be enough to pull down the filament supply. This amp has a bad history. Maybe a shorted output tube cooked one or both of these resistors. Usually that causes an increase in value but not always. I have seen toasted resistors decrease in value too, sometimes to nearly short-circuit. It's also possible that some modification "expert" installed a part that's not the right value. For instance they might have put in 1 ohm instead of 100 ohm. As long as the filament center tap is working those balancing resistors are not necessary - in fact they would have no effect at all - unless one or both were shorted or very low ohm value.

[Wil]

Both are in the service manual I previously sent.
I replaced those resistors a couple of month ago. There is continuity with or without the center tap wire. But there's no sound when it isn't wired. (or there has to be a big input signal to hear a scratchy horrible distorted sound, just like when you set the bias of a fuzz at the minium, you see/hear what I mean ?)
I did not check if there's a difference without the resistors. But do you think they can induce a ground loop ?

Edit : WOW! I just cut the two resistors and I had really really strange noises coming from the amp. In standby mode, so I believe they aren't useless!

Edit 2 : Answer from Mercury Magnetics :
Hi Romain,

Unloaded, the 6.3 should measure 3.15 each leg to the center tap.
Meters can vary when not isolated, and I believe you are within spec as long as the amp sounds good and performs as normal.
Keep us posted.
Thanks.

Patrick

I get 2.8VAC at each leg.

[Leo_Gnardo]

Wil: <Both are in the service manual I previously sent.
I replaced those resistors a couple of month ago.>

and since then, possibly a shorted output tube sent excess current through them and they changed value.

Wil: < There is continuity with or without the center tap wire. But there's no sound when it isn't wired. (or there has to be a big input signal to hear a scratchy horrible distorted sound, just like when you set the bias of a fuzz at the minium, you see/hear what I mean ?) >

That is bizarre, no sound without the CT wire to ground. Let's make sure we're talking about the right one. Filament CT is usually green with yellow stripe. Mercury's color code may be different. In any case, IF the "balancing resistors" were working, and the 6.3V CT was disconnected from ground, the amp should work without any unexpected noises or distortion.

Wil: <I did not check if there's a difference without the resistors. But do you think they can induce a ground loop ?>

It's not a ground loop I'm worried about. If one or both resistors were low ohm when installed, or changed value to low ohm when burned due to output tube fault, that could be drawing excess current from the 6.3V winding and causing it to sag badly. Also could cause random changes in filament voltage.

Wil: <Edit : WOW! I just cut the two resistors and I had really really strange noises coming from the amp. In standby mode, so I believe they aren't useless!>

Heard really strange noises, output tubes installed or not? Rectifier tube installed or not? From the speaker or from the amp itself? Did you measure the ohm value of those resistors? With tubes removed from amp (all of them) what AC voltage do you read from 6.3VAC and 5VAC wires.

I'm trying to do everything I can to prove whether the PT is broken before you spend money on a new one. These are really strange symptoms.

Last time you ran this amp past MEF "panel of experts" you said there was a tech somewhere nearby. He may be expensive BUT we have given you the best advice we can, and spent many hours doing it. It may be time to let your local amp expert sort it out for you.

Another thought, you want to get the sound of an original Deluxe Reverb. Even with a DRRI running perfectly, it's not really the same thing. You mentioned thinking about putting in a Hoffman circuit board. I have done that on several amps and they worked out well (59 Bassman reissues, 50W Marshall RI's, and Vox AC30 RI's). Reliable, and excellent clarity of tone. Expensive, and even more if you need a new PT, but I think that's the closest you will get to "the real thing". And it takes a good tech some time to do it. Adds up to a pile of Euros. The best techs in the world have gone round and round with you and this amp. If it doesn't clear up soon, be prepared to dig deep into your pockets and pay your local tech to get it done right.

[frus]

Wil, does your transformer hum when you turn the amp on (without tubes)? I don't mean hum from the speaker, I mean a soft physical hum in the transformer itself. listen closely in a quiet environment

[Dave Curtis, dB AudioTech]

You are all assuming that Wil's meter is good.

Wil, have you checked the filament winding on another amp that works as has been suggested? What does it read?

Balancing resistors on the heater winding also can serve as fuses in the event of a heater-to-cathode short in a tube. They'll burn open rather than burning the heater winding with the CT grounded... Also, if they were 1 ohm, what would you expect the heater voltage to be?

Check the meter, Wil. What does a fresh 9VDC battery read? How about the heater winding in a known good amp? Perhaps you know someone that can lend you a meter so you can compare readings? I keep a bunch of meters on hand for this very reason.