Bogen chb35a and Bogen chb100

[DüTerra]

I'll get straight to the point as this will likely be a long post...

I have the two Bogen amps listed in the title. The chb35a seems to be all original, the chb100 supposedly has had a few capacitors changed and a small mod or two although I haven't had time to confirm this yet. Also note that the chb100 looks like it caught fire at some point.

I already have like 10 amps so I don't need another one. BUT... I figure the blown chb100 has to be rebuilt anyway so I might as well build something for myself.

Going forward, my plan is to restore the chb35a and convert the chb100. But as these simultaneous projects progress with help from your collective wisdom this plan is subject to change.

More specfically I want to convert the chb100 into a 100w bastard (probably) version of Rob Robinettes Blackvibe:

https://robrobinette.com/RR763_BLACKVIBE.htm

The reason I say bastard is because to follow his schematic exactly I would have to buy tube bases for the 12ax7 plus the bases for the 6l6s and extra 6l6s. I already know that I am not the most fond of 6l6 anyway soooo. I think I will keep the odd tubes and base the Blackvibe around the stock tubes and stock circuitry. But this is an area where I'll be asking for opinions and advice.

As for the chb35a I am inclined to restore it. It seems to be in really good shape with all original parts (I think). It would have the original tubes too but I sold them for a pretty penny ~5years ago. I know that no one really cares but part of me wants to restore it for history or something, idk.... Maybe just so there will be a Bogen ready to covert for the next generation or something, again idk.... If it weren't in such good shape I probably wouldn't care so much. What can I say? I like that the chb35a has input for a record player so I would like to have this for use with my record player. Maybe I'll ditch the old solid state Pioneer! Haha. I've read these aren't particularly good for phono applications in spite of having that option.

In conclusion, earlier today I went through the entire chb35a with the schematics just to take note of any deviations. There were one or two but I suspect that the differenes were due to the schematic not being the proper revision to match my particular version of the amp. I plan to go through the entire chb100 tomorrow in the same fashion. Soon after I'll update with pictures and info.

I know that I could use some 1/4" jacks for the input and speaker outs. I could probably use some new capacitors too. Maybe you all could help ensure that I don't leave anything obvious out whenever I am putting together a bill of materials?

I also want to check all of the transformer before I place any orders or move forward with planning.
Any insight or advice from you all would be greatly appreciated.

[mozz]

I've converted these to guitar amps before, they often use a voltage doubler in the power supply and/or a 6v rectifier. I can't see the purpose of restoring a mono tube amp for home use? Pull the 6eu7's and make in a fender, easy enough.

[DüTerra]

"I can't see the purpose of restoring a mono tube amp for home use?"

Is there a difference in a "mono tube amp" and a tube amp for home use, specifically for a record player?

This is all fairly new ground for me.

[tboy]

"...specifically for a record player?

Most people would want a stereo amp for that purpose, but if you enjoy hearing your records in mono the Bogen will do a fine job, You'll need to mix the left and right channels if you have a stereo turntable, though.

[DüTerra]

Most people would want a stereo amp for that purpose, but if you enjoy hearing your records in mono

That makes perfect sense.

How much more difficult would it be to convert the Bogen into a stereo amp?

[Jazz P Bass]

"How much more difficult would it be to convert the Bogen into a stereo amp?"

You need two of the Bogen amps to make a stereo setup.

[DüTerra]

You need two of the Bogen amps to make a stereo setup.

Alright well, I have 2, one chb25a and chb100. Admittedly I have enough guitar amps. So this is an intriguing idea. If I took this could one still be a functional guitar/bass amp?

[g1]

If you convert it for guitar use, it generally won't sound very good for hi-fi use.

[DüTerra]

Ok so a stereo hi-fi seems like it's going to be too much trouble. I'll probably just turn the chb100 into a guitar/bass amp. The chb35a might follow the same path or I may simply restore it and keep it as a P.A. for vox. I can't decide yet but that's ok I don't want to get ahead of myself.

I feel like the smart thing to do now is to test Power & Output Transformers in both amps to get a better understanding of my situation, ball park figures on cost, etc.... Am I on the right path here?

Regardless, I started doing research on how to perform transformer test last night. It is taking me a little while to figure out how to perform these tests with just the DMM and soldering iron I have on hand. Gonna try to get this figured out and transformers tested by the end of tomorrow to keep this ball rolling.

[DüTerra]

I got the power transformer unsoldered from my chb100. It's still mounted onto the chassis but all leads were removed from the circuit.

Check my terminology in this next part:

The primary? wires: going from transformer to fuse to on/off switch to cord.... measured 1.6ohm. I tested each to ground as well an got OL.

The heater? wires: going from transformer to power tubes to pre tubes and the "on" light.... measure .4 ohms. Each measured the same .4ohms to ground as well..... bad sign?

The other winding that went to the rectifier diode... measured 4.6ohms. OL to ground.

Seems to me there is a short to ground inside the transformer, is this correct?

[Enzo]

Seems to me there is a short to ground inside the transformer, is this correct?

Where? You get open circuit to ground from the primary, you get open from high voltage winding to ground, and the heaters are a low number of turns with heavy wire, it will always measure very low resistance.

Put your meter on ohmss, and touch the probes together. What reading do you get? That is the resistance of your probe wires.

[DüTerra]

Where? the heaters are a low number of turns with heavy wire, it will always measure very low resistance.

I thought that the heaters to ground where supposed to read OL too, is that wrong? It's good to know they'll always be low R. Thanks for the info.

[Enzo]

Your heater winding has a center tap that is grounded.

[DüTerra]

Right on. That's great news. With a transformer that size maybe I'll build a champ in the style of Randall Smith from Mesa.

[g1]

I thought you had disconnected all the transformer wires. Did you leave the heater center-tap wire connected?
Or Enzo , are you saying the heater CT is internally connected to the TX frame?