Troubleshooting Deluxe Reverb - Where do I start

[LoveChet]

I have a 1979 Silverface Deluxe Reverb.

Before I started this repair job it was sounding good and all working properly but evidently running on only one 6V6 since one 6V6 was drawing no idle current when I checked bias. I gues they can run only one 6V6. I knew I had 6v6 tube socket issues so I figured it was a good time to change them out. I assumed that would fix the one 6V6 idle current/bias issue. I also figured was good time to change the 25 uf preamp electrolytic caps on channel 2.

I made the changes and checked all the wiring several times. All good solder connections.

When I turn in on the 6V6 tubes glow however the amp is totally dead. Not a whisper, crackle, or pop. No magic black smoke either.

Where do I start with diagnosis. I don't have a signal generator or a scope. I can check voltage however.

I knew there was a reason why I avoided turning it on for a few days after making the fix.

Just one more turn on the road to success.

spkr is plugged in

Thanks in advance

[Enzo]

Start like any dead amp - check power supply voltages. Make sure speaker is plugged into correct hole.

[LoveChet]

Took out the head. hooked up spkr and reverb cables, plugged it in, !!!!!!!!! Now it appears to be working since there is a little hum.

With 6V6 tubes in their sockets, both measure 440 VDC on both plate(3) AND screen(4). Control grids(5) -35 VDC

What do you think is happening ??

Thanks - Gary in Western Mass

[überfuzz]

What do you mean when you write, appears to be working?

Cheers!

[pdf64]

It should be disclosed that the amp has been extensively modded ;-)
Failing switching contacts in the fx loop return jack are a common cause of intermittent signal loss.

[LoveChet]

Before the 6v6 socket switchout the amp was operating fine, sounded good. all controls worked. Fx loop worked as well.

Its just that one 6v6 was not operating so it was going on 1 cylinder but sounded ok, maybe little weak.

After the switchout it was dead but then when I extracted the head to debug the dead amp, it was working at least some hum so I know its not totally dead like it was.

Its not the fx loop contacts that are the issue since it was dead even with the fx loop deactivated.

Questions:
1) What other thing could cause it to be intermittent.
2) Is 440 VDC on both the plate and the screen proper ? Both 6v6s measure that with tubes plugged in after the socket switchout.

[g1]

How are 6V6 sockets pin 8's connected? Straight to ground?

[LoveChet]

Pin 8 Cathods are soldered directly to chasis with a 1 inch braided wire.

I was questioning the 440 VDC on both plate and screen since I thought scematics showed them as different but I rechecked a schematic and see that they are the same as in
415, 415 as an example. I see where your going maybe with the cathode wiring question since a resistor from cathode to ground would cause a voltage drop across it and make plate and screen different (I think).

I'm a electroinc tech from way back but never delved into amp wiring and maintence until just this week.

Incidently I must have a poor connection as in spkr jack maybe which is why it was dead and then came alive.

More to follow

Gary from western mass USA

I'm 77 and hope I live long enough to get this modded Deluxe back in shape so I can practice Chet tune. I am getting it to sound pretty good after all these years.

[LoveChet]

All is well. My modified Deluxe Reverb is back in working order. It must must have been poor spkr jack connection. I cleaned it up.

So, my first amp repair went successfull. I changed out the 6V6 tubes sockets and evidently put the wires back properly. I also changed the channel 2 preamp cathode electrolytics.

Gary from Western Mass. Thanks for all the help.

[pdf64]

Well done in finding this fault
Not sure if you've been advised of this previously, but a key part of a major service on these things is to re-establish the numerous mechanical chassis connections that allow the chassis to properly function as the amp's 0V bussbar. The issue is surface corrosion / tarnishing, crushed star washer, loose fastener, anything that prevents a very low resistance path to the chassis.
Anywhere that has a thread which clamps through the chassis, a star washer and a solder eyelet (eg all jacks, pots with a soldered body, most importantly the mains ground bolt) then remove the fastener, clean the chassis metal around the hole until it's shiny. Check that the star washer still has sharp 'teeth' and replace if not. Refit fastener, star washer etc and tighten up the fastener sufficiently for the star washer to 'bite' into the chassis (ie the teeth marks are apparent if it's removed).

[LoveChet]

Thanks pdf64

You have reinforced what I should have done already in that if you don't cover all the basics, then eventually you will have issues. You gave a great explanation of how to make all the proper grounds. That will be my next maintenance task.

I have learned the hard way that you need to clean tube sockets, replace tube sockets, buy new tubes, play with different tubes, adjust idle current using proper bias.

In doing all these things then you ward off the situation where you have an issue and you immediatly think you have a bad component somewhere. Not that it can't happen and I havn't had that happen to me yet but I always worried about it.

Now that I know how great my deluxe can sound I won't settle for anything less.

Thanks again