Bias/balance question for Blackface Super Reverb

[Newguy]

Need Help

opto-isolator, how does it go in?

It has the two longer leads and dot (should be optical right)
Other end short leads (should be resistance side right)

1. I "think" resistance side should go closest to tone knobs.
2. I "think optical side goes closest to back of amp?

Am I right?

I do not see a dot on the current opto.

*As amp sits now, the two solder connections closest to vol/tone knobs, one is grounded, the other is connected to Intensity pot.

Please advise.

House current 127 volts. Verified with second meter Pete.

Have 1 ohm resisters and getting ready to solder them in.

Thanks for jumping in here Dave, but you will have to dumb it down quite a bit. I just started reading about this tube amp when I started this thread. I am taking baby steps here, but hope to learn something, and at the same time fix a couple small problems with this amp.

[g1]

You are correct. As shown in the schematic, the resistive side connects to the pot and to ground. The bulb side goes to the other connections (nearer to rear of amp).
With regard to contact cleaner: the pots need lube, the sockets don't like it. You used contact cleaner with lube for both. Try to clean any residue off the sockets with isopropyl alchohol.
The method Dave described is a safer alternate to shunt biasing. You are measuring at the same points you used when shunt biasing (centre tap of output transformer to pin 3 of each tube). First you measure the resistance with amp off (but preferably warmed up). Write down the value for each side/tube. Then you measure the voltage at same points with amp idling. Volts divided by ohms equals current. This method does not require the current range on the meter.

[Dave Curtis, dB AudioTech]

Thanks for the clear-up, G. The 1 ohm cathode resistor method is even safer, although initially more involved (to install them). Make sure they all measure as close to each other's value as you can. The nice thing is that once they're in, they're there for the next time you set bias.

[Newguy]

Man, I did not know you could leave the resisters in. No matter, not that much trouble

Pete, special thanks for jumping in on the opto for me to replace, best $15 I ever spent (resisters and opto part $15).

G One, thanks for post last night, I did not want to put opto part in wrong and I was getting ready to give up for the night when you posted, glad you were on board.

Opto install was a sucess. Tremolo not real strong, but about the same as my "Deluxe Reverb RI". Sill, I get lost in all that Reverb and Tremolo.

Notes:

1. I had to take meter back to RS, then again, acting flaky and would not even read a/c wall voltage. Funny thing is, found same problem on their unit they used in shop when they tried to read wall outlet. Got another cheap meter at Lowes for $30. At least readings seem stable.

2, Guy who brought me opto part and resisters said resisters where hospital quality and he measured 4 resisters out for me at exactaly 1 ohm.

My meter read them all at .8 Ohm, and my old analog meter looked to read about .9 Ohm.

OK Here are my readings doing it the cathode resister method, leaving every thing the same as when I adjusted it last time using the shunt method.

1. Reading across the 1 ohm resister 33.7/33.9.
2. Plate voltage chassis to pin 3 465/466.

Observations:

1. Doing it the shunt method, readings say I have more Bias (40 mv approx), but less plate voltage 454 approx, and calculations say about 18 watts.

2. Doint it the Cathode resister method, reading say more plate voltage (approx 465), but ma/mv reading at (approx 34). Which means about 16 watts I think.

Interesting. Unless I hear funny noises/blow fuses, or some one here says something is terribly wrong, I will leave as is as it sounds fantistic.

I was able to turn it up loud the first time today, sounds sweet.

Thand you all for the help..and my next post I hope some can help me with ssr to tube rectifiers.

[Newguy]

Need help

Pete (you brought it up), or any one:

How much trouble is it to go from the solid stare rectifier (parts on tube socked) back to the orig tube rectifier?

Any links to directions or pics?

How much does a decent rectifier go for, a decent one, not an expensive one..if that is possible?

[pdf64]

I don't understand why your plate voltage should be higher with the 1ohm resistor than with the current shunt - maybe your wall voltage had increased between the tests.
Whatever, I'm pleased that it's working out well for you.
The tube rectifier should be as simple as removing the Si diodes and plugging a tube in.
Assuming that the diodes are fitted between pins 4 to 8 and 6 to 8? Could you post a photo?
You should be able to buy a current production GZ34 for $20. Lord Valve seems to have a good reputation as a tube vendor over there - his site is down but give him a call, see link for phone #
About our Tubes
Used old production tubes are worth considering - I bought my Vox AC30 in 1982 with a Brimar GZ34, it was old then, may even be the original one from 63, and it's still working fine.
Keep the Si diodes - there's an alternative way of fitting them so that they automatically back up the tube rectifier, and protect the power transformer, if the rectifier tube ever shorts.

[Newguy]

Pete

I will work on posting a pic. I took a bunch of pics when I had chassis on kitchen table, so it is a matter of posting here, may have to reduce size or something. I am interested in what members here say about condition of parts. Looks to be all original to me. I do not see any ruptures or any thing like that. I am sure it needs a cap job, but I do not feel the need yet, unless members see pics and say replace this or that cap/resister. I took the bottom plate off also to take a look see at big caps, they look orig also, with no ruptures.

I do not understand the difference in readings either. However, when I did the shunt reading, I had a Radio Shack meter (had to take it back as it went crazy on me), replacement was no better.

Now on the readings (last night) with the resisters method, I used a meter from Lowes, also not the best I am sure.

I did not touch the bias adjustment pot last night. I only took readings.

I will post pics soon.

Going back to a tube rectifier sounds pretty easy (with your help of course lol).

Thanks

[Newguy]

Pics, hope you can see socket well enough.

[Newguy]

More Pics

[Newguy]

Even more pics

[Newguy]

Note pic 5707, the external speaker jack, it has wire (hanging). It may be because part of jack broke, and rather then replace, they just rigged it so that wire was not needed?

Hope the pics help, let me know what you think as far as what it will take going to tube rectifier tube and what is needed, as well as what you see as far as condition of caps/resisters

Please guys, all chime in

Thanks

[Newguy]

Any one have a link to the mod PDF talked about concerning rectifier socket?

It appears I have diodes pin 4 to pin 8 and also diodes pin 6 to pin 8.

I think all I have to do is cut diodes out and install tube (which BTW I already have and did not know it, as I had backup for 65 Deluxe RI and it also takes a 5AR4/GZ34)?? It is a Sovtek.

I am interested in using the diodes I cut out to "back up" the rectifier socket in case of rectifier tube failure.

Thanks for any help

[Dave Curtis, dB AudioTech]

Note pic 5707, the external speaker jack, it has wire (hanging). It may be because part of jack broke, and rather then replace, they just rigged it so that wire was not needed?

It looks like someone disconnected the negative feedback loop for a little less clean. Kinda odd that diodes were put in to get more headroom when the NFB is not there...

Hope the pics help, let me know what you think as far as what it will take going to tube rectifier tube and what is needed, as well as what you see as far as condition of caps/resisters

Thanks

The cardboard-covered caps are the original electrolytics, and you might want to consider replacing them in the future. 44 years is a bit past retirement for a 'lytic. I'd leave the other stuff as is 'til it causes a problem. As was previously mentioned, you can leave the diodes in and slap a rect tube in it... I don't recall if the power supply caps were changed or not. If you're going to use a tube rectifier, make sure those are upgraded. I usually replace the power supply resistors with flameproof parts while I have the PS caps out. I also do the same with the screen resistors.

-DC

[Newguy]

Dave, are you 100% positive I can leave the diodes in as is and just slap a rectifier tube in?

PDF posted

"The tube rectifier should be as simple as removing the Si diodes and plugging a tube in"

"Keep the Si diodes - there's an alternative way of fitting them so that they automatically back up the tube rectifier, and protect the power transformer, if the rectifier tube ever shorts."

Complete post below
I don't understand why your plate voltage should be higher with the 1ohm resistor than with the current shunt - maybe your wall voltage had increased between the tests.
Whatever, I'm pleased that it's working out well for you.
The tube rectifier should be as simple as removing the Si diodes and plugging a tube in.
Assuming that the diodes are fitted between pins 4 to 8 and 6 to 8? Could you post a photo?
You should be able to buy a current production GZ34 for $20. Lord Valve seems to have a good reputation as a tube vendor over there - his site is down but give him a call, see link for phone #
About our Tubes
Used old production tubes are worth considering - I bought my Vox AC30 in 1982 with a Brimar GZ34, it was old then, may even be the original one from 63, and it's still working fine.
Keep the Si diodes - there's an alternative way of fitting them so that they automatically back up the tube rectifier, and protect the power transformer, if the rectifier tube ever shorts.

[Dave Curtis, dB AudioTech]

quote from the diyAudio forum:

"To provide some additional protection for the rectifier tube you place the diodes in series with the plates, cathode end to rectifier plate."

-DC