Wonderland/JM100 build

[martin manning]

I'd leave them long just because. I like to cut off any bare wire, fold the end back a half-inch and put heat shrink over that. Then bundle all the unused leads and zip-tie them.

[norburybrook]

Ok.

fired up full power.

main B+ voltage to screens is 520vDc

the dropping string is 520-507-460-460vdc and the tap to the reverb is around 500


I've got 450vdc on the plates of the pre amp valves.


this is all without valves.

should I put valves in now and re check or are the voltages too high at the moment?

marcus

[ToneMerc]

I would install the preamp tubes and recheck. Also, I would install a 120-150K 1W bleeder resistor from B5 to ground to pull down the preamp voltages even more.

TM

[norburybrook]

ah like you do when you don't use the FET on an ODS special build

Marcus

[JazzGuitarGimp]

Personally, I would start wth the output tubes; get them installed and biased, then reasses wher your B+ is at.
Edit: However, if you haven't already done so, check the range of adjustment of the Bias supply, and make sure the bias voltage can be measured at pin 5 of the output tube sockets, then adjust for full negative voltage before you install the output tubes.

[martin manning]

Why subject the preamp valves to such abuse? I'd put the power valves in, and the 150k bleeder, and see if a satisfactory bias point can be achieved.

[norburybrook]

I would install the preamp tubes and recheck. Also, I would install a 120-150K 1W bleeder resistor from B5 to ground to pull down the preamp voltages even more.

TM

Actually there's a 220k from B+5 to ground already there. Do you mean add another 150k?

Marcus

[martin manning]

You can stay with what you have for now and tweak preamp voltages later.

[ToneMerc]

ah like you do when you don't use the FET on an ODS special build

Marcus

That's the reason the 220K is to the right of the B5 node cap on the power board. In planning my JM build I initially was going to leave it off so that I could run slightly higher voltages at V1, but then I made it switchable.

Since your build will be at least 30-35 volts or so north of normal voltages, it will not hurt to use a smaller bleeder value.

TM

[ToneMerc]

Why subject the preamp valves to such abuse? I'd put the power valves in, and the 150k bleeder, and see if a satisfactory bias point can be achieved.

I was being cautious, if something goes south, preamp tubes are cheaper than a quad of power tubes

TM

[norburybrook]

OK, I've got 492 on the plates so to bias the 6L6's 30w max 60% cool bias

30x 0.6/492= 36mv

correct?

Marcus

[martin manning]

Yes, and the plate voltage will drop a bit so you are safe with that. Don't forget to set the bias at the most negative voltage position before powering up with tubes in and be sure you have a load connected to the output. Use the limiter too if you want to be really safe.

[norburybrook]

-77mv is as far as I can get.

What do I need to change the resistor to to get me in range?

it's 27k on the pot and a 1R on the rectifier board.

M

[martin manning]

This is a problem. I think you will need a doubler circuit to get enough bias voltage. I think you have room for another diode and another cap.

[norburybrook]

there's plenty of room on the rectifier board. Could you do me a layout Martin so I can see what and where i need to put things?


Time to remove the rectifier board for the third time it seems as I'll need to drill and add eyelets.


can i ask; if the transformers came out of a working amp how did peavey get enough negative voltage to BIAS?

Marcus