Custom Kraft 600 amp info needed "pics"

[jr_vw2]

If anyone can lend some info on this custom kraft Model 600 (not a 600a) I would love it. I cant find a schematic or any information on this amp. I am trying to find out what tubes it takes because they are all rubbed clean. ANy info would be great. thanks

http://i28.photobucket.com/albums/c241/jr_vw2/5182_3.jpg

http://i28.photobucket.com/albums/c241/jr_vw2/4bfe_3.jpg

[WaltC]

Well it *looks* like it *might* be a fairly common for the period AC line amp using the 35W4 rectifier, 50C5 power, & 12AU6 preamp tubes w/ a field coil speaker (using the field coil in the middle of the chassis) and a choke. These amps were nothing to write home about even when new, and that one is *rusty* in the field coil and choke so could have some serious leakage (*not* something you want to mess with since the amp is basically connected to ac line voltage w/ no isolation but a fuse!). I'm no Custom Kraft expert, but based on the condition of the cab, chassis (rust & crud) and the type of amp it was to begin w/ I'd recommend a good recycling center or convenient dumpster.

You might be able to clean it up, wash the faceplate and gut the chassis and convert it to a decent sounding champ-style amp (w/ a replacement speaker), but only if the wood is in good shape.

Sorry for the critique, but I've just recently restored two similar (Airline, Vox) amps and was definitely not impressed.

[bunuel]

Well it *looks* like it *might* be a fairly common for the period AC line amp using the 35W4 rectifier, 50C5 power, & 12AU6 preamp tubes...

It's almost certainly those tubes (& they're cheap & easy to find)--I've had a coupla of these little custom Krafts. Though, I happened to really like how they sounded, sorta like a nice tube screamer with a speaker. Per previous, be careful with 'em, they can serve up a nasty shock!

[jr_vw2]

Thanks guys. I am not really interested in the amp for use per se. I am more intersted in just fixing it. I am reading and doing all I can to try and verse myself in amplifier electronics. I basically want to just see if I can get this amp working. It seems like a very simple circut. It has a REALLY bad hum in it, the caps are testing bad in it. Could i use a gerneral amplifier replacement speaker in this of does it have to be this exact style? THanks again

[SatelliteAmps]

You can use pretty much any speaker in that thing. Should be amusing when it is done.

[WaltC]

Thanks guys. I am not really interested in the amp for use per se. I am more intersted in just fixing it. I am reading and doing all I can to try and verse myself in amplifier electronics. I basically want to just see if I can get this amp working. It seems like a very simple circut. It has a REALLY bad hum in it, the caps are testing bad in it. Could i use a gerneral amplifier replacement speaker in this of does it have to be this exact style? THanks again

The way this amp works won't help you too much in understanding "normal" tube amps, but I guess every bit helps. The caps are probably causing much of the hum, but the rusted laminations on the choke could be contributing quite a bit as well.

Any small speaker should work...

[SatelliteAmps]

It's not a field coil speaker, and I kind of doubt that is a choke. A field coil speaker runs off a B+ supply, and has at least four wires going to it. Two for the signal, and two for the electrical supply for the magnet.

It's hard to tell exactly, but it looks like the AC is going directly to the larger of the two transformers, which would make it more of an isolation transformer, rather than some huge choke. Those types of amps will always have a little hum to them, because there is little filtering and no chokes usually.

I also wouldn't worry as much about the rust on the transformer issue. It's not a noise causing issue. These amps can be made into little screamers really easily. They have a low-fi sound, but it is pretty cool. Don't throw it away or recycle it without at least trying it stock.

Do you have any pictures of the actual guts? That would tell exactly what those both are.

[jr_vw2]

Well I replaced the caps in it. I couldnt find a multi with the values I needed so I used individuals. Still couldnt get exact but I got it close enough. The amp is dead quiet with ZERO hum in it now. It doesnt seem to have much output though, I am pretty sure the speaker is shot. it is only measuing 0.6 Ohms But I also have no idea what Ohm rating the OT is set for.

SateliteAmps----- Can you give some advice on how to turn this into a "screamer" As of right now the sound quality is pretty poor. However it is quite good with a distortion pedal. But I still dont feel that the amp is quite up to par.

The power cord goes to the Pot and the Transformer.
the big oranger firecracker is gone now replced with three individuals.

http://i28.photobucket.com/albums/c241/jr_vw2/575e_3.jpg

[SatelliteAmps]

Your speaker is shot if it is reading .6 ohms.

Good job replacing the caps. Using individuals is fine if you can't find (or afford) a can cap replacement.

Those tubes will only put out 2 or 3 watts max, so it won't be insanely loud, but it can be made to sound good. Having a working speaker is probably the first thing to take care of. I am guessing it was probably a 4 ohm originally, but an 8 ohm would also work. I would also make sure there is a bypass cap on the bias. If there is, I would replace it with a new one. If there isn't one there, then I would add one. Electrolytic. Somewhere between 33uf-50uf, around 100 or 150v should be fine.

After that is working, and if you want to get more involved, I would take a look at the capacitor that is feeding the volume and the tone control. That one looks pretty old. If it is and has gone off value, it will raise in value. That will make the amp more bassy, less gainy. So those would be next on my list to change to new versions.

If you get this far and it isn't enough, there are a few other things to do, but my guess is that should really make the amp come alive. Keep us posted.

[WaltC]

yup, good input Adam, my bad on the field coil and iso. makes much more sense than choke (didn't look close enough before I opened my mouth <G>.

One thing to do is the check the coupling caps for leaks and check the values of the plate load resistors, the silvertone I just finished had an open 2.2meg plate load resistor on the second half of the 12AU6 and so no sound was getting beyond the first pre-amp tube. Someone had (before it got to me) unsoldered the speaker leads for some reason and the owner brought it in for a replacement speaker. Speaker worked fine though and after I put in a new 2.2 meg it perked right up and worked fairly well. Nothing to write home about, but took a signal and made noise <G>.

[jr_vw2]

Here is an update on this little amp. I added a 12AX7 to the amp and now one input runs the the 12AX7 then into the 12AU6 and the other input runs through the 12AU6 only (stock) Thought I might post pics of the almost finished product along with a sond clip. (yes I know the vol pot is hanging loose in the pic) I have some Oxblood grill cloth on the way as well as a Fender style handle to finish it off.

Demo (http://s28.photobucket.com/albums/c241/jr_vw2/?action=view&current=100_2569.flv)

http://i28.photobucket.com/albums/c241/jr_vw2/Fireball.jpg

http://i28.photobucket.com/albums/c241/jr_vw2/100_2570.jpg

http://i28.photobucket.com/albums/c241/jr_vw2/100_2573.jpg