Some one gave me parts from an old Leslie 122 ?? guitar amp maybe

[copperheadroads]

Did some digging & found a discussion about this over on "the Amp Garage" forum

https://ampgarage.com/forum/viewtopic.php?t=6237

[copperheadroads]

Shouldn't this work or am i missing something ?
http://www.valvewizard.co.uk/bias.html

[loudthud]

Looks good to me.

[copperheadroads]

Looks good to me.

whats the value of the first unnamed cap ?

[g1]

The unnamed cap is part of the HT circuit and independent of the bias circuit (as would R3 be).
The unnamed cap could be a totem pole arrangement or whatever filtering you use for your first B+ node. R3 would be the bleeder for that cap(s).
In your example of post #13, it just shows 'B+', the unnamed cap and it's bleeder resistor is down that line somewhere and not shown for the bias circuit purposes.

[loudthud]

Be advised: If you are going to install a Standby switch, it should be after that first cap and bleeder resistor. Otherwise, the bias circuit won't charge up while the amp is in standby mode.

[copperheadroads]

I have a on/off /standby switch here that I've trying to understand how to wire it buy if it gets complicated i may omit & for get the standby all together .

[copperheadroads]

Just a thought .. i have a quad of sovtek 5881 tubes that i may consider using for this build is there any concerns about using them ? my output transformer is 4000 ohm & only a 16 ohm secondary .
& will i have to change anything in this bias circuit? i'm following the valvewizard schematic & I only have one of those Marshall style 22k trim pot & the schematic calls for a 47k pot will the 22k pot work ?

[copperheadroads]

Be advised: If you are going to install a Standby switch, it should be after that first cap and bleeder resistor. Otherwise, the bias circuit won't charge up while the amp is in standby mode.

I've noticed in the train wreck documents the Bleeder resistors ,are referring to the 9.1k resistors ? , I figured the bleeder resistor are the 2 100k's resistors going to ground at the 47uf filter caps .

Here's the layout i as roughly following

[loudthud]

The bleeder resistors refers to the two series connected 100Ks to ground. The 9.1Ks are what I call the series dropping resistors. Some people might call them decoupling resistors. You can use an 18K for the two connected in series. If you can't find 9.1K, use two 18K in parallel (9K) or a 10K and 100K in parallel (9.09K). Someone built an Express clone while Ken was alive and ask Ken why it didn't sound right. Ken listened to the amp over the phone and said he could hear the difference between 10K and 9.1K resistors. That's some powerful mojo

[copperheadroads]

Well were all done & I got it done without the standby switch for now & powered it up without tubes for the first power up , Dimbulb is ok (no shorts)
time with voltages are high , 523v negitive bias can go from -10 to -29.5v but turning the 22k trim pot . Heaters 7.2vac .
with the tubes in the amp ,i get sound & the tubes glow but not redplate but the filament in the dimbulb starts to slowly glow just a little bit .I'm not sure sure if its a short as the only bulb i can find was a 250 watt bulb . but with all knobs at 0 i faintly hear a high pitch squeal so I probably have to swap the leads on the Plates on the OT ..
I'm wondering if it's an actual short in something or should i proceed ,,Cant smell anything heating up .

[loudthud]

-29.5V seems like not enough for 6550s. Referring to the schematic in post 17, you might try increasing C1 to 220n, R1 to 100K or R2 to 22K or 33K. Are you using a 47K or 50K pot for P1?

[copperheadroads]

In this the crucial previous post ,I am using the typical Marshall 22k bias adjust pot & for this first power up i'm going with the trainwreck I've tried a new set of JJ'S 6ca7's as I have no 34's if you read back I want to use a set of 5881's but lets get her running with this first . we can bias for the 5881's later .
I've tested the old 6550's on my tube tester & they tested in great shape .

[copperheadroads]

What about the dimbulb with the slight glow ? . is it a short .. I felt like i should swap the OT primaries & let her buck .

[loudthud]

Hard to tell with a 250W bulb. I would expect some kind of dim glow, but any kind of short would be a bright glow. What worries me is the limited bias Voltage. You may just have to try it and shut it down if there is too much current in the output tubes. Hope you installed 1 Ohm resistors or have a bias probes. Try disconnecting the feedback and make sure the Presence control is at zero. The Express has a lot of gain and really wants to oscillate. If it is inconvenient to swap the OT primaries, swap the wires feeding the pin 5s of the power tubes.