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It's fairly normal for the amp to make a lot of noise when you touch the plate resistor like that.

I've looked at the photos and I don't see anything out of the ordinary. Are the input jacks wired up correctly? Is pin 8 of the 6V6 grounded?

Pin 8 on the 6v6 goes to the 25 25 cap that is jumpered with the 470- 5 watt resistor which is grounded as per the layout diagram. Yes the input jacks are wired correctly.

My brain feels like it's about to explode studying this thing. I disconnected the two leads coming from the jacks to the 68K resistors and it makes no difference. But with my fuzzy brain I don't know what purpose that served. I'm guessing I've got a direct short as it sounds like when an amp is turned on with guitar cord plugged in to the amp but not to the guitar, then touch the tip of the plug and hear the noise.

Edited: I disconnected the ground wire from the bridge rectifier and all noise went away but still no sound from a plugged in guitar. At this point I think I'll have to scrap this project as I know nothing else to do.

Danny,
Try posting about this on the music electronics forum: http://music-electronics-forum.com/f22/ They've been helpful to me with some projects.
Mel

MWaldorf wrote:Danny,
Try posting about this on the music electronics forum: http://music-electronics-forum.com/f22/ They've been helpful to me with some projects.
Mel

Thanks for the suggestion Mel, but I'll pass. If Mr. Bill has no further thoughts on what to do then I'll scrap this project as it is beyond my comprehension.

I post over at MEF all the time. There are a lot of helpful folks there.

Mel, did you ever get the Vox replacement board to work? I've been thinking about using one to get an old Berkeley head working again.

Dub, When you say that the sound is like having a cord plugged in the input but not being plugged into a guitar, that is what makes me believe that the input jacks could be the problem. Use an ohm meter and test to be certain that the ground connections are making a good connection to the grounds of the rest of the amp. If the chassis is painted it may be keeping the grounds from being made. While you are at it, check all of the separate ground points for resistance to the main power supply ground that you disconnected.

Thanks Bill, I did check the input jacks with the meter as well as all the grounding connection. Plus, I sanded all grounding areas down to bare metal then ran a separate ground wires from the jacks to a ground lug getting zero reading.

There is no reason on gods green earth why this thing should not work unless it's a fault in the diode rectifier assembly. The entire project is extremely simple to be so confounded frustating. This damned thing is causing me chest pains.

I appreciate all the help but don't feel obligated to reply any more as I think all possibilites have been exhausted. I'll get it out in a few years and have another look.

Like you said, this is a simple circuit, so you should be able to get it working.

The bridge rectifier is producing voltage like it should, so there is no problem there. Please test and post dc voltages at each filter cap, at pins 1, 3, 6, 8 of the 12AX7 tube.

Oh, and did you test the ground on the volume control?

Yes I did test the ground on the volume control and it was fine. After allowing it to warm up for a while the voltages settled down from my earlier high readings.The main filter cap reads 330v, the second reads 235v, the third 204v, on the 12AX7, pin 1 reads 114v, pin 3 reads 1.0, pin 6 was 137v, pin 8 reads .99. BTW, pin 8 on the 6V6 reads 27.3v

I may have smoked something as I really screwed up. I should have quit before I got so brain tired today as I spent from 8am to 9pm at the work bench in deep concentration trying to trouble shoot everything possible including unsoldering removing the board, input jacks, volume control and then reinstalled everything. And.... after all that, with the amp unplugged, voltage bleeder wire hooked up from ground to the first filter cap, power switch on to keep voltages bled off, thinking I was plugging in the soldering iron instead I plugged in the amp. Shortly after I heard sizzling and it went dead. I did this two other times throughout the day only blowing a fuse each time. Lesson learned, never ever work on an amp when you are brain dead tired. Hopefully it only blew the fuse again and not something more serious. I shut it down for the night as I am too tired and will check for damage tomorrow.

Edited: I fired it up this morning and everything is alright, just hums like a buzz saw but still won't play. Funny thing, when testing the voltages again I could faintly hear a radio station through all the hum and static while touching the meter probe to pin 8 on the 12AX7.

If you turn the volume control all the way down does the hum go away or lessen?

If you pull out the 12AX7 tube does the hum go away or lessen?

Yes, never work on anything electronic when you are tired or distracted. I've been zapped a few times in my life, always when I wasn't paying attention.

The sound is quieter with volume turned all the way down then gets really loud as the volume is turned up. With the 12XA7 pulled out of the amp the noise (sizzling, humming, popping) gets louder and worse.