Bell & Howell 385 (08855)

[Appaloosa]

B&H guitar amp project

Hi, I just stumbled onto this thread. I realize its a couple months old, but I was curious how your B&H project turned out? I also have a couple of B&H 08855 that I would like to turn into guitar amps. Your drawings look great, and I was wondering how your amp sounded if you got it together. thanks for all the help.

[Raja]

I got busy with other projects and haven't put it back together.
I just about have it gutted and will have some time to work on it soon.
Have you played through your amps? How do they sound?
I found some errors on mine that I think were causing the hum. The heaters were wired incorrectly and there were some areas of concern with the grounding of the amp.
My drawing hasn't been proven yet so it's not to be trusted. I would leave your filter caps alone for the time being and look at the filament wiring and grounding on the amp and clean those up first, if they need it.
Raja

[guitician]

The first stage pentode could be eliminated by using just the three gain stages of V2 & V3. Increasing the plate resistors on the first couple of 12AX7 stages would be required and if more gain is needed, just add cathode bypass capacitors. It would reduce noise, and may sound better too. IMHO

[Appaloosa]

Thanks for the response. I have not yet plugged my amps in. they are still in their "original" state. I'm somewhat of a newbie to this and I was wondering the best way to attack them? I was thinking i would just plug one in and see what happens, but I don't have the original power cord or the right size speaker out jacks. So I figured if I needed to get in their just to replace the power jack and spk. outs I might as well chop out whatever else is not needed for guitar use. Then I saw your schematic and thought about going deeper while i had it apart. do these amps sound good left original? thanks for the help and info!

[guitician]

I would say by looking at the pics that they are not good for newbe's. They're way too compact to work on. If you just use the transformers and chassis as a start, then re-arrange the tube placement and component layout adding terminal strips as needed per the redesign, you may end up with a really nice guitar amp. The filter capacitors will need reforming if it hasn't been powered on in years. Two 6V6GT, 5Y3GT, and a pair of 12AX7's are the ingredients of some great amps.

[Raja]

Appaloosa,
I would do the minimum necessary to just hear what you've got to work with. In your photos the back amp has a note on it that said it was blowing a fuse and if in the other photo of the gut shot the back amp is the same then someone has made changes to the amp. Two of the caps are not original but they are in the section of the amp not needed for guitar, but the brown variable resistor (10 W/500ohm) has been changed. This resistor should be set so pin4 @ V4 reads 325 VDC. If you remove the unnecessary components from the amp that resistor will need to be adjusted.
If it was me I would start with the amp to the front in your photos and find a power cord that will work or change it out and rig a speaker up to it and see if it still works. V6 is not needed for guitar amp but I would leave it in and I would also leave the PEC tube in but would blind it by wrapping black electrical tape around it.
When I bought mine I also got an extension speaker with it so I was able to adapt a 1/4" plug to it easily.
These amps were meant to be used with a loud film projector and hum was not an issue.
Let me know if I can be of any more help.
I'll update when I get further along with my amp.
Raja

[airplaytheremins]

Hey Raja,
I can't see the attached thumbnail with your schematic and parts omitted for the amp to function for guitar. Can you repost?

[Enzo]

Raja hasn't logged on since Feb of 2014, he may not get your message.