Amp conversion

[consoleb]

I have a Bogen CHB 10A amp and I want to use it for guitar. The two inputs are a single phono input and a screw on mic input. The mic input has three wires and the phone input has one wire and is grounded to the chassis. The speaker output jack has three wires. What do I do. I am handy with tools and know enough not to get zapped by a capacitor. I will be changing the electrolytic capacitors. The amp has not been plugged in for a long time and I want to tune it up before use. Any feed back will be welcomed.

Thanks

consoleb

[doc]

I would suggest changing the filter capacitors, test the tubes on a tester (if available), then bring it up on a Variac (if available) slowly without the tubes, then with only the rectifier tube, then with the signal tubes in. Have a number of appropriate fuses on hand. In other words, see if it works first before any mods. Run a signal to the phono input (unless you have an old mic with appropriate cable) and see if you get an amplified signal from a connected speaker. If not you have some diagnositic work to do (you can at that point just change all the small electrolytics first and see if that fixes it, or do that before trying it out if you plan to change them all anyway).

[Structo]

Those are cool old and very moddable amps.

Here is the schematic for your amp.

http://www.schematicheaven.com/hifiamps/bogen_chb-10a.pdf

Notice the mic input. I would run a 1 meg resistor off of the input to ground, which creates a 1 meg input impedance. This is what guitar amps use.
Add a 68K grid resistor in series after the .01uf cap to the grid.
Get rid of the 3.3Meg resistor on the input.
Then change the bias on the first tube to more of a Fender type by taking a 3.3K resistor and a 25uf electrolytic cap in parallel from the cathode to ground.
That should get it sounding more like a guitar amp.

[consoleb]

Thanks for your help.

consoleb