New Pictures of everything is located at - http://www.flickr.com/photos/8486416@N02/sets/72157630387243290/

I see a lot of spaghetti and a lot of stuff not on the original schematic. This is heavily modified!

On the two tubes that went red plate the bias resistor is cooked. The resistors on the two remaining bias resistors are 15ohms. I get the math now using ohms law (I = V / R). So my voltage should be .75 (750mv) with a 15 ohm bias resistor on each tube. If my bias resistor was shared then I would halve this number. Now the really strange stuff:

- all my tubes are missing pin 5 (I think but looking at schematic it must be pin six missing)
- pin 1 is not connected to anything on every tube
- pin 4 had a 30 ohm resistor before going to the transformer on every tube

On the pull down resistor I see a 22 ohm resistor off of pin 5 to 6 (one of these pins is not is use - see above bullet) and them wires are going from pin 6 to the unknown board. It looks like it is connecting to the white and green cap and green resistor that you see on the top picture of the amp (example right side right of the right 6922 tube up front). Then there is a series of three blue resistors. I will have to look at it later tonight to determine if this is where point 21, 22 and 23 is (or 1, 2 and 6). I am assuming if these are on this board then they may have accounted for that.

Looks like my first task will be to replace the two fried resistors. When the amp last went red plate it sounded fine, if that means anything at all. Looking at the two tubes that went red plate (happened about a week apart) the silver at the top of the tube is less than the other two tubes, so I am guessing best case I have just lost some life on them. I do not see any other burnt electronics. Could the tube socket get damaged, because the pin 8 seems lose?

There is a Repair sticker on the bottom for some place in Oregon (503-284-8693). I am calling them later today.

I think I read the resistor wrong on pin 5 to 6 it must be a 1k (brown black red and not red red black) and it goes to the resistors and Cap I mentioned before.

looking at the pictures the resistor I thought were 22 and 23 to 21 may not be the ones.

the 1K resistor from pin 5 to pin 6 is correct. 15 ohm cathode resistors are fine, so yes, set your bias to read 750mv across each one of those.
Setting bias is usually interactive, which means you'll have to keep re-adjusting a few times as changing one will influence the others until they are all very close to the same amount.
Pin 1 and pin 8 on each output tube should be tied together (screen grid and cathode) then thru the 15 ohm bias resistor to ground.
The 33 ohm resistors on pin 4 tied to the OPT should be fine, that's just added protection.

Thanks tubes4hifi this has been a great learning experience (and some re-learning) - What is the bottom line impact of not applying the negative bias to the grid (pin 1 - grid no. 3)? I need to replace the two burned out resistors and tie in pin 1 before I can test it out. I am hoping I have not fried the two tubes that were on the burned resistor circuits. I think I was running the amp with one burned out resistor for a while without it red plating. I had the bias turned back on that tube though. I definitely fried those resistors by having the bias up too high. Weird part is I had been running the amp for sometime with the high bias, but I think I was running the volume much lower.

Added pictures of the top of the circuit board and noticed transistors (link at the start of the post). I guess I have a Hybrid - LOL

Will a 1/2 watt resistor be OK? I calculate the watts at .0375 when I have the bias correct on 15ohms per tube. However should I be as low as 1/8 on the idea that you want the resistor to burn out if you get a run away bias, so nothing else fries? However the amp was still playing when the the resistor burned and it did not seem to stop anything. I do need to check the resistor when I pull it out to see if it is allowing any current through.

I recommend that you change all 4 of those resistors to 10ohm 1% wire-wound resistors. The wattage is not that important. You can get them from Mouser for about a buck apiece.
http://www.mouser.com/ProductDetail/Vishay-Dale/RS01A10R00FE12/?qs=NmlBeBNZel40XkxyugdQpeY%252bm6ctSkJqvwtDFt6GE1k%3d

hawaii.ken - Thanks for the replay. Funny you recommend that. I went to Radio Shack and picked up some half watt 15 ohm and got some one watt 10 ohm since there was no one watt 15 ohm in stock. That would make my bias voltage half a volt then. The 10 ohm ones are metal film blue color resistors.

10ohms would give you .50v at 50ma per tube.

I recommend 36ma to 44ma per tube.

Thank you to everyone who gave me help to debug and fix my amp. I replaced all the bias resistors with one watt 10 ohm metal-oxide ones. I like that my voltage is my amperage now by a decimal place. Running at around .333 for now and keeping an eye on red plating and voltage. After I see that it is stable I will take it up to around 44ma. I still need to tie pin one and eight off the tube to the bias resistor. What is the impact of pin one not going to bias resistor? I plan to put pin one into the circuit, but for now I was just wanted to get it back to how it was running before I cranked the bias to high. Oh that tube sound - soooooooo sweet.

What a felling fixing it yourself:) Makes me want to build one from scratch.

Ran it for about half an hour at medium volume. Bias settled at .45 to .43 between all the tubes after half an hour and at idle. It sounded great!

Thanks again

It would be a good idea to re-tighten the socket mounting screws to ensure a good connection to ground for those bias resistors.

The screws are very tight, however some of the socket pins are lose in the base. I need to check that they are tight on the pins, but it took some effort to plug in the tubes.

I knew something was strange when you set your bias to 1.56v with 15 ohm cathode resistors, you probably could have fried an egg on your power transformer...

Sal