Hammond Organ Amp to Guitar Amp Conversion Project

[Structo]

I do have a 4H 90ma choke but it only has a DC resistance of 105 ohms.

I have a set of drawings by Billy Yates that shows either a 1K 5 watt or a 5H 100ma 100 ohm choke.
Does the inductance of that choke make it equivalent of the 1K resistor?

That drawing uses a GZ34 rectifier.
I don't know squat about tube rectifiers as I've only used diodes in the past.
I'm thinking I need to use the 5U4 tube because of the voltage present which is 380-0-380.

Can somebody tell me anything about these rect tubes?

[Structo]

On the AO 29 schematic it shows the field coil as 700 ohms.

[skyboltone]

Would adding a choke input filter equivalent to the field coil drop the voltage and stiffen the supply enough to use 6l6 tubes or just drop voltage enough to use 6V6's without sounding harsh ? If so what value would you suggest SBT ? Does anyone know the inductance or dcr of the FC speaker ?

700 ohms on the field coil. Dunno the inductance. 115MA

[mark enger]

any imfo on the ao 43 chassis iv got one and a couple of extra pts. is there a 6.3 ct or does it need 2 resistors to ground to make a ct

[skyboltone]

any imfo on the ao 43 chassis iv got one and a couple of extra pts. is there a 6.3 ct or does it need 2 resistors to ground to make a ct

I've seen a couple of those over the years. I don't know what they came out of. Maybe an L or H model. They don't differ much but I don't think they used field coil speakers. If there is a filament CT you will be able to measure it each brown to it (probably green) and get the same resistance. But I have seen lot's of Hammond PTs without CT on the filaments. The old timers did a variety of things to combat filament hum most importantly a 25uf bypass cap and low gain. If you are going to make a virtual center tap, use a pair of 100 ohm resistors. I always measure them on the low range DMM setting to get a pair that are as close as possible.

[mark enger]

there is a green wire thats common to the heaters. i assume it is ct

[skyboltone]

there is a green wire thats common to the heaters. i assume it is ct

yeah.

[Structo]

Have you received the expression control yet Dan?

Are you going to reimburse me for the postage?

I'll pay postage for your un-needed expression control and e-mail you the file on how to do the buck program. How's that?

[skyboltone]

Have you received the expression control yet Dan?

Are you going to reimburse me for the postage?

I'll pay postage for your un-needed expression control and e-mail you the file on how to do the buck program. How's that?

What a memory I got. Yes! Sorry. No I haven't seen it. I'll go back to my messages and do it instanter.

Done! Again, my apologies.

[Structo]

Thanks!

[Structo]

OK I have this thing cobbled together.
I used a schematic I found on the internet designed by Billy Yates.
I didn't want the traditional Deluxe with the two inputs so this one makes the second half of V1 another gain stage as well as use a long tailed pair PI.

Right now with just the rectifier tube (5U4) plugged in I measure 465 vdc on the plate pins for the 6V6's.
That is coming right off the first 40uf cap in the string.

Way too high. I am trying to use the 6V6GT tubes that came with the Hammond and I don't want to risk those until I get the voltage down.

Pin 4 (screen) seems to be in the same ball park which surprises me since that comes after the choke, which is a 4H @90ma choke.

I also added two 470R screen resistors.


According to my data 6V6GT have a VaMax of around 350v.

That is the first data I have but when I look lower it says for AB1 P/P
it says 285 with a bias voltage of -19v.

What would be the best way to drop that voltage to a safe level?
Should I aim for the 285 since this is a P/P amp?

I'm thinking a 10 watt resistor off of the 40uf cap?

The good news is that my heater voltage is low at 6.15 vac.
All I did to that is ground the center tap for the heaters.
Plus I am using a #47 pilot light.


Right now I have the two 10K resistors on the JJ cap can I have (40uf, 20uf, 20uf, 20uf).

Should I leave those alone and put a resistor in front of the choke?

Here are the schematics I am using.

[Structo]

I should also add that the voltages I mentioned above were with a 60 watt light bulb current limiter on the power line.

[skyboltone]

One ho made tool I really encourage folks to have is a bunch of 1K 20 watt resistors layed out in series on a heat resistant board. FR4 is fine. Then you can test power supply circuits with real world loads. You need about a 40 watt 6K load across ground and the + end of the first filter cap. This will place an appropriate load on the power supply for the idle current through the screens and plates of a pair of 6V6GT. If you model what you've done on Duncan's power supply software I think you'll find that loading the PS will drop the voltage to well within limits. Afterall, that's what Hammond used.

[Structo]

Holy Crap!

So it needs to be 40 watts?

The biggest I have available is 10 watt.

Do you think the power tranny could handle 6L6's?

I tempted to drop in a couple Sovtek 6L6's I have laying around.

[Structo]

I tried using the Duncan PS calculator and when I plug in my values of full wave tube rectifier, 4H choke, 40uf cap and a 6K load, it errors with
" The rectifier PIV of 1,500 has been with a value of 1,593 at time 0.0428."

What is wrong with my values.
I'm not sure what to enter for the resistance on the tranny and capacitor.