[willisv]

Quote:

Originally Posted by miky /img/forum/go_quote.gif You mean made amp o to put some resistors across the 1 & 3 wires? What about 7.1v for EZ81 JJ? It's ok?

I had about the same (14-14.5V), I used a 5W 4.7R resistor to drop the voltage to 12.16V. The resistor will go inline on one of the wires.

 

[runeight]

Quote:

Originally Posted by Listen2this1 /img/forum/go_quote.gif Ok I have been following this thread for a while. I think I am going to reward myself and build one over fall break. I have a couple of questions though. How close can I mount the power supply and the amp boards? I have read that they need to be seperated but have not seen a actual distance suggested. If I mount the tubes externally how much heat will be left, and can I mount Q1 and Q2 on the enclosure. Does someone have the spec sheet on the tubes? Like diameter and height. I have a enclosure, and I am wanting to place it in this. It was initially fot MHM and I decided to go another way. I will be doing this for a final project in class. I hope that all parts and materials will be in a 3-d model, all the way to the diodes. James

Listen2this1, there is no really hard and fast rule on the spacing. But, at least 2-3" apart IMHO. When you choose an enclosure, try to arrange for as much spacing as you can get.

You can mount the mosfets on the enclosure but remember that they are at high voltage. They need to be insulated, but I would also recommend that you somehow arrange things so that they are not easily accessible to fingers and tools. MHO is that it's better to put them right on the board with their heatsinks. That way you won't be at as much risk of touching their pins and you won't introduce parasitic capacitances into the regulator circuit where it might cause HF oscillations.

If you mount the tubes through the top there is very little heat left inside. Just a few power resistors and the mosfets.

 

[amphead]

Pabbi, I removed both amp boards which consist of the right channel, and inspected your wiring scheme to ensure the ground mod could work the way it's intended. Looked over the daisy chains for heaters and grounds, and they will work just fine. Reinstalled amp boards, so now to remove PS boards for the "actual" mod. Edit: purchased two 10 watt 100 ohm resistors for the ground. Call it superstition to use those, but they worked well on my amp.

 

[pabbi1]

Watching the surgeon at work... hope you are getting to listen a little on the way - is the sound changing, assumed for the better from burn in?

 

[amphead]

Yes, there has been a steady increase in resolution. It would give me more volume however, if I hooked up both power supplies before listening. One PS set of wires were not hooked up on todays session after wiring up the right channel boards. Late nights take their toll. I was surprised that it even worked! It's alot louder with both power supplies hooked up. Still working on the ground mod.

 

[runeight]

Say, amphead, do you still have 250V from both regulators?

 

[amphead]

Oops, gulp......373VDC out of both supplies. Edit: chalk it up to tunnel vision to have trusted the PS regulation. This is some design, to have taken a beating like that and still sound/work great! Edit: it seems to resist my attempts to reduce voltage on both supplies. I have been turning both pots counter-clockwise a few turns, power-up, check, power-down etc......Edit: with both pots turned fully counter-clockwise, one PS is at 350VDC and the other at 335VDC. Alex, do we run in the overvoltage condition safely? It behaves normally otherwise, save the strain it is probably putting on some amp board caps.

 

[chobint]

is that 373vdc loaded or unloaded?

 

[runeight]

Quote:

Originally Posted by amphead /img/forum/go_quote.gif Oops, gulp......373VDC out of both supplies. Edit: chalk it up to tunnel vision to have trusted the PS regulation. This is some design, to have taken a beating like that and still sound/work great! Edit: it seems to resist my attempts to reduce voltage on both supplies. I have been turning both pots counter-clockwise a few turns, power-up, check, power-down etc......

WHat is the input voltge to the regulators?

 

[amphead]

I can access pin 3 of the rectifier tube, but access to say the positive terminal of C4 would need to have a wire soldered to the bottom of the board......

 

[runeight]

You can get this voltage by measuring at the exposed lead of R7.

 

[amphead]

Ok, 505VDC and 510VDC on R7 for both supplies.

YGPM

Pabbi, did the amp have 250VDC B+ when it left your place?
Never mind, I found the answer:
Quote:

Powered up, after about 10 minutes still getting a solid 248v on each side (no rebiasing), and all tube heaters came up nicely. Getting the same result - attenuators work, R & L are equally operational, well, at the barely audible level. Oh, and the hum is definitely there - faint, but enough to notice.

Damn! I blew the regulators(at least that's my analysis of the situation) when it ran with one PS hooked up. :holds head down in shame:
No worries, I'll get those from mouser. I wish I had ordered extras, when I ordered mine. I think I ordered these:FQP4N50

 

[runeight]

These voltages are way, way, way too high. C4-C6 are over voltage and are going to fail. Don't run the amp or ps any more at these voltages.

There must be something wrong with the transformer, rectifier combination. What is the AC voltage on the secondaries?

 

[amphead]

Some fantastic news! Sorry guys, just not enough sleep lately. The meter was low on battery power and I didn't notice that. Voltages at R7 ~330VDC, and more importantly voltages at supply outputs around 220VDC, with pots fully counterclockwise. I will dial it in tomorrow, after a good nights sleep. That meter was giving me a coronary!

 

[adamus]

keeping us on our toes amphead. I was going to suggest the meter, you would have seen caps blowing at those voltages.