Deluxe Reverb RI bias question

[Newguy]

Are the left & right 6V6 matched (+/-5mA)?

"That does not seem correct but have no time to look it up. Amp sounds fine." If the amp really sounds fine, then it IS correct. However, most old/NOS 6V6 don't tend to like plate & screen voltages above 425vdc, modern 6V6 (typically all 14W GT rated) don't mind the higher voltages. If you want to stick with the NOS try bumping up the current until the plate voltage comes down...then have another listen.

You can't play your guitar when the OT is being shunted, if you want to play whilst setting bias buy some bias probes.

No, they do not seem to be matched?

I am not getting any current on the right tube socket when viewed from back (blue wire on pin 3). I had another set of 6v6gt's that were microphonic to test in socket. Same deal, no current on second tube.

Amp still sounds good (I guess I like one tube). I noticed the amp was sounding better to me after I had a 6v6gt get microphonic on me (maybe something going bad). When I changed the tubes I liked the amp more and more. That shows how screwed up my sense of tone is.

What is likely bad part? It would seem if I have current in one socket (left one with brown wire), I should have current in the other? The funny part is when made the mistake on pin3 of tube socket and MWJB said to change tube, it was the tube socket on left with brown wire to pin3, and that seems to be the good one? The right tube when viewed from the back is the one with no current.

I plan to let cool then check pin 3 to ground on each socket. to see if I have plate voltage on the socket in question.

I also plan to ohm out pin 3 on that socket to make sure it is not the actual socket?

Should be cooled off, going to check to see if plate voltage is present on right tube socket.

[MWJB]

"What is likely bad part?" Output transformer.

[Newguy]

"What is likely bad part?" Output transformer.

MWJB you are still on the forum..great.

I was hoping for something cheap. How much does an output transformer go for, how much labor about? Tech I recently talked to in area (opening a new shop), I think he said $25 per hour bench charge. That is AFTER he knows the problem, he does not charge for troubleshooting.

I checked pin 3 on both tubes and getting about 420 vdc each socket/tube.

I used ohm meter and socket in question pin3 ohm's out top/bottom. It was set to 435 but not sure if I got orig tubes back in, and only gave it a minute or so to warm up, just wanted to check voltage.

Amp still sounds the same. Maybe it has been gone for awhile if OT, or maybe I fried it by putting meter probe in wrong test point? Amp has sounded different (for better in a strange way) over the last couple months. I thought I was just getting speaker broke in as I have not played that amp all that much over the years (bought it new in like 94).

Thanks for your help.

[Newguy]

MWJB is this the correct replacemnt:
Fender Output Transformer, '65 Deluxe

I saw some wanting around 100 bucks. The above says genuine Fender.

Is there any reason, if it is the OT transformer, to go any thing more heavy duty then the fender one? The $39 one in link seems like a deal compared to the $100 ones, but some of those were not Fender.

This will be a job for a tech. I just recently found one in area that works out of his basement (he is opening a custom guitar shop also). Worth a shot as local GC I hear is not that good (who ever they send it to).

Is there any other possibilities for this problem or is this pretty much a 100% call. IE, is there any wires that could be loose causing this (a bad connection that could cause only one side to work..I take it that is what you think problem is).

Just asking as if there is something else I can check I have it apart now.


Thanks again

[Newguy]

MWJB

I see why you suspect the OT transformer, it goes to pin 3 of each 6v6 (brown and blue wire).

Can you explain why I am getting 420 vdc on both sockets pin 3 but no current (ma) on pin 3 on the one socket.

Brief...dumbed down version, as I have little understanding of a tube amp.

Thanks

[Enzo]

Your current measurements are being made to determine the number of milliamps flowing through the tube. Trust me, the current will only flow the right direction. SO it really doesn't matter which meter probe goes to which point. Red probe to center tap adn black probe to plate OR black probe to center tap, red probe to plate. The reading will still be in milliamps, and if the probes are "backwards," you simple get a reading of negative current. But since we KNOW the tube will not be conducting backwards, all we care about is the amount, not polarity. Follow?

Now then, when probing those plate leads, your meter probes can be like large antennas. And those antennas can radiate back into the amp circuits, basically a form of feedback One plate will be opposite in signal polarity from the other, so one will represent negative feedback - a stable situation - but the other will represent positive feedback. At least potentially.

I have found many times that I can probe one tube with the shunt method, but the other won't give a proper reading. I suspect the side that won't read is causing high frequency oscillations. You can't hear it, it is RF, but it prevents a proper reading. Try reading with the meter away from the circuitry, and the probe wires as far from the rest of the circuit as possible.

And sometimes just reversing your probes can help.

You got two tubes, and one seems to have no current? Pull the tube that does have current and see if the amp works with only the "dead" one. If the amp functions, then we know that side is conducting current, even if we can;t measure it.


When you put your CURRENT meter from a plate to ground - that red/yellow stripe wire is grounded - you essentially shorted the B+ to ground. No wonder you blew the amp HV fuse. But you are darn lucky you didn't also blow the current fuse in your meter.


And 6V6 vs 6V6GT. Are your tubes recent production tubes? Or are you using some 40 year old tubes. If they were made in recent history, consider them GT whether it says that on them or not.


ANd a good rule of thumb is when you get a mysterious reading when trying to measure something, try measuring it a different way. For example, unground pin 8 of the "dead" tube and insert a 1 ohm or 10 ohm resistor from pin 8 to ground. Now measure voltage across that resistor while the thing is running. That is what a bias probe does.


And as to taking bias readings while pl;aying, or rather trying to play while measuring bias, as soon as any signal runs through the amp, any reading you take is no longer "bias." it would then simply be a tube current reading, a reading of little value.

[Newguy]

ENZO

Thanks for reply. I have a feeling the amp may have ALREADY had a problem with only one tube working (although with current reading on net, it is said OT's do not go under normal operation conditions). About a couple months ago, got strange type of noise out of that amp. I quickly swapped out power tubes and noise went away. The amp, to my ear started sounding better (very slight distortion if you will, but seemed to be very musical..got fat faster at lower volume, which is a plus to me). Now this. I would not have known there was a problem if MWJB had not asked if tubes were balanced/matched, as I forgot to check both tubes. Both tubes were a nice red tiny glow, both looked exactly the same, both looked normal and still do.

Now, amp sounds exactly the same. Both tubes have the little red dot where you can see the red, and both look the same. Now I see there is no current going through the one tube.

*Also, the main thing I am not sure I mentioned, the one tube is hot, where the other tube only gets a little warm. I could expect a bad reading on the meter if I had not found that the one tube only gets a little warm (I can touch the tube and it does not burn, it is not hot enough, I can just hold my had on the tube, only warm).

Today I tried another (older) set of 6v6gt tubes and the same socket is not getting current (ma). However, both are getting about 420 vdc pin3 to chassis ground.

I admit, what I did was a stupid move. It is very possible I fried the OT with that stupid move. However, I am not convinced I fried it?

I have been thinking about this, and read a thread here on this site, where guy left Deluxe Reverb RI on stand by while on break. Came back amp was dead. He had bad OT, and it took out some more stuff. He was not sure if the OT was the problem, or if something else went first and took out the other stuff.

All input welcome. I am thinking maybe it is a good idea to replace rectifier tube also when I take it into shop, as well as have guy go over the amp from top to bottom. I want new Tung Sol reissue 6v6gt tubes also, but am wondering if I should spend money before I know amp is solid again?

[pontiacpete]

Did you try the one tube test that Enzo suggested?

[Enzo]

And if in fact there really is no current through one tube, see if the B+ is missing from its SCREEN pin.

[Newguy]

1. Did you try the one tube test that Enzo suggested?

Well in a way, yes I did. I replaced both tubes with two other "different" tubes I had, same exact problem. I did this as I was thinking a small possibility that the one assumed good tube could be causing problems, long shot I know, but figured I would try. I am not a real tech, but I built mini computers for years in the 70's-80's (board level only), and have seen some strange things. I am a good parts swapper.

2. And if in fact there really is no current through one tube, see if the B+ is missing from its SCREEN pin. Enzo, you will have to explain that one, I do not know what the screen pin is. Like I said, pin 3 to chassis ground is getting about 420 vdc. Pin 3 is plate voltage though...correct?

Also, when checking screen voltage, where to I ground dvm (chassis I assume?). Do I just use the vdc scale?

Keep in mind I did take tube out, and ohm out socket on pin 3, there is a connection at pin 3 from bottom to top.

3. I am kind of stuck on the bad tube socket not getting hot to the touch (with two different tube sets), as well as no current being able to measure with dvm. If the tube is not hot, it is not working.

** Are you guys fishing to see if something other then the OT is the bad part? If so, what do you suspect?

It is easy enough to swap out the tubes again if youg guys want. I put the amp back together, but easy enough to take it apart again if you think there may be another fix. I have my electric drill on charge right now as just got amp back together, and just barely had enough battery for the screws. It may be another hour before I get enough charge to disassemble again.

Let me know what other items you would like me to try...if any?

Also, if all you guys think it is the OT like MWKB suggested, how hard is it to replace the OT. By looking at it, it appears to be a piece of cake. 4-5 wires and two screws. Let me know if I am wrong on this, as it sure looks easy. Hate to spend $55-$60 on OT if it is not certain to fix the problem.

I will check back soon as I am cleaning up all my mess here with tools, tubes, and other stuff.

[Newguy]

Enzo

Reread your post, I see I had a couple things to do:

1. You got two tubes, and one seems to have no current? Pull the tube that does have current and see if the amp works with only the "dead" one. If the amp functions, then we know that side is conducting current, even if we can;t measure it.

Nope. I strumed guitar, and got a little static type sound out of speaker, but that was all.

2. Tubes recent production (at most 20 years old).

3. And as to taking bias readings while pl;aying, or rather trying to play while measuring bias, as soon as any signal runs through the amp, any reading you take is no longer "bias." it would then simply be a tube current reading, a reading of little value.

I was wondering why no sound at all from speakers when I strummed guitar?

**Observation: Since you guys are experts, this may give you a hint. I had dvm set to ma, 1 probe to pin3 of bad socket, 1 probe to Red wire, but of course getting no ma readings.

I went to power down amp, and hit standby first, I noticed meter readings going up in ma pretty fast (probes still in same place). I hit power switch as thought this to not be normal, and did not want to give it a chance to do damage.

I just played amp for a while. Sounds great lol. Like I said, I am not sure blew the OT if that is problem. Not the type of guy who would try to say..hey, I did not do it, I just want you guys to look at possible other causes. I did make a total blunder by putting probes in wrong place, very possibly causing damage..and if nothing else, just being stupid.

I noticed on last set of tubes, it had the Russian logos and such. One tube looked like real good logo and print quality, while the other looked like a lot was missing. Possibly the one tube running hot, possibly just the way the tubes were made? Just more information to ponder.

[MWJB]

Quick test, power down & unplug from the wall. Measure ohms from pin 3 of both power tubes to CP14 red wire, are the dc resistances about the same?

Once the chassis is out an OT can be changed in 30 minutes, so you''ll probably pay minimum bench fee, plus price of part. But CONFIRM that the OT is shot before buying a new part, or going to a tech. Lots of people make "Deluxe Reverb" OTs, some are made to different specs & in different parts of the world...this is reflected in their prices. Hyboer are a trusted & reliable brand, usually supplied by Mojotone.

[Newguy]

Quick test, power down & unplug from the wall. Measure ohms from pin 3 of both power tubes to CP14 red wire, are the dc resistances about the same?

Once the chassis is out an OT can be changed in 30 minutes, so you''ll probably pay minimum bench fee, plus price of part. But CONFIRM that the OT is shot before buying a new part, or going to a tech. Lots of people make "Deluxe Reverb" OTs, some are made to different specs & in different parts of the world...this is reflected in their prices. Hyboer are a trusted & reliable brand, usually supplied by Mojotone.

MWJB

Please help me along with the Confirm of the OT being shot. It is very late here, could not sleep. I will take amp apart today when wife gets up will ohm out pin 3 of each tube to CP14. it only takes me 5 min. or so to take chassis out.

You have an idea I see, what are you checking for?

Have you heard of these guys:
Fender Style Transformers

Good price, made in USA. I will check out Hyboer/Mojo and check prices. A few bucks here or there is not a huge deal, if in fact it makes any tone difference. The link above say they are made like the old style and sound good? Any truth to one OT sounding noticeably better then another?

I would prefer taking to a tech for this. However, I live in sticks. I have a guy in mind though and hope he returns my email and phone call. AND, hope he is good.

I do not see a problem with me replacing OT if I can not get this tech contacted. Looks easy. Is the OT soldered to chassis, it does not appear so. I do not have soldering iron strong enough to do chassis work. I see 5 wires, 2 screws and a couple solder connections, looks easy.

One question. I played amp for about 20 min. Then left it sit there for a couple hours (turned on). It seems to work fine, and sounds good (I am sure it would sound stronger if working right).

Thanks for sticking with this thread.

Thanks again for help.

[MWJB]

"You have an idea I see, what are you checking for?" If one side of the OT primary is seriously shorted then this will show up as a low dc resistance compared to the side that is not shorted. For a working OT there may still be a little difference, but a large discrepancy is not good.

I have used Magnetic Components transformers. OTs can sound different (like other components they may be made with differeing materials & to differing specs), you are after a drop-in replacement for a DR, if this is made to the DR spec it will be adequate, as will about a dozen other options...if you are after the "best" OT you need to determine what you don't like about the one that was in it (before your troubles started) and buy one that is "better" in that respect (whilst eliminating all the other variables like B+, tube brand, bias, speaker, etc.)...deciding which one is best (as with most components) usually means auditioning a few, which means that you won't be concerned about keeping costs down ;-) I'm not aware of any manufacturer who says their transformers sound bad? :-)

[Newguy]

MWJB

OK

OHM readings pin 3 of each tube to CP14. You did not say, but tubes were left in for readings.

Left tube= 200.7 ohms.
Right tube=200.3 ohms.

Left socket is the good one, right socket is the bad one. Looks like the exact same readings on each side as meter jumps around a tiny bit.

Hope you are still on forum this morning.

Yea, I am looking for a drop in replacement with costs down. Tech in area has not returned emails or phone call as yet. May give him another call/send another email this morning.

I may be doing this myself if tech does not call back, and you guys are pretty sure of the part that is defective.

Thanks