Just got this Bogen Challenger CH8 working, now what?

[Brokegunner]

I was in here maybe 6 months ago and you all were very helpful answering my questions on my Mod 102+ I built for my brother. I've been gathering parts for my first "home brew" build but haven't had time to really start on anything. So last week this guy contacts me because he knows I rebuild old radios and he has a bunch of mostly junk but mentions he has an old guitar amp. So he brings out this Bogen Challenger and says they are expensive on ebay but to make him an offer... so I got this for a very reasonable price.

20230512_172716.jpg

I found a schematic online and I had all of the tubes in my stash. I thought it was odd that the multi section can capacitor was 4X4uf caps, was expecting them to be bigger. I installed a terminal board near the can and wired in 10uf 450v radial caps. I replaced the old wax caps but all of the resistors were within spec. I'm getting voltage readings that match the schematic, so everything is good now.


I've got maybe 4 hours in it total now and it's sounding great. I'm using a wireless Bluetooth device from my cell phone to drive it so I don't know what it will sound like with a guitar.

Here's a photo of the underside before I installed the fuse holder and the pilot light:

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Here's a pic of the finished amp:

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[Brokegunner]

Ok, so now that I got that posted with the photos, I have a question for the experts here... how can I improve this amp? I have a huge stash of 12AX7, 12AU7 and 12AT7 tubes, and I have plenty of 6SN7 that might be a better tube than the 6SJ7 in there now.

The current tube lineup is 6L6 output, 6SJ7 preamp and 5Y3 rectifier. There is a 6VA6 but that was for the mic input and I removed the mic input. I don't have any experience with audio amp design...I guess I should start with the data sheets and see what I can figure out but I thought I would ask if anyone sees an opportunity here and can give me a hint.

Here's the schematic that I found online that someone drew up. There is a resistor value that didn't match my amp but having this was very helpful.

Bogen Challenger CH8 - rev A.pdf

So if anyone has any suggestions on what would be a good way to go with this. My plan was to build a clone of a fender 5F2A from all the parts i have collected but now that this dropped in my lap, I'm wondering if I should just rewire this amp to match that circuit?

Thanks

Brian in NorCal.

[Stevem]

Improving it is relative to what you think it’s lacking!

Why don’t your Brother or both of you play it a while and first see how you like it.

That cabinet or amp in the background of your photo looks like a Univox B45?

[Brokegunner]

Improving it is relative to what you think it’s lacking!

Why don’t your Brother or both of you play it a while and first see how you like it.

That cabinet or amp in the background of your photo looks like a Univox B45?

Hi Steve, wow I had no idea it has been 10 months since I was working on this amp!! I guess I got busy and set it aside to consider my options and this week I finally grabbed it off the stack and decided to work on it.

I don't play guitar and my brother is far away so I have a friend at the local Cigar Lounge that leaves his guitar and amp there all the time and plays on weekends. I had him play it for a few hours and he liked it but it didn't have much volume and the tone selection was disappointing. He also played my MOD 102+ kit amp and he liked that one better.

This CH8 has a 6AV6 and 6SJ7 feeding the 6L6. This morning I removed the 6AV6 socket and installed a 9 pin socket in its place so I can wire in a 12AT7 or 12AX7 (I have a lot of 12AT7 here from my ham radio repair hobby).

The part I am not sure of is if I should keep the 6SJ7 in the circuit? I have looked at a lot of schematics on the 5F2-A and the AA764 so I am getting familiar with how things go together. The Champ AA764 has a 2 pot tone stack which seems to fit this chassis better, but the tone stack is in between the 2 sides of the 12AX7 preamp tube.

There is a channel on youtube called D-Lab Electronics and I have been interested in his videos because he does a lot of ham radio equipment. He did a video on this exact same amplifier and replaced the 6AV6 with a 12AX7 and also swapped the 6SJ7 for a 6SL7 (requiring a rewire of the socket) and he designed it so either preamp tube could be installed depending on what kind of sound you want. Well, in his testing video they concluded that it sounded best with both preamps in at the same time, which was not what he expected when designing it. I wrote and asked if he had a schematic for this as he usually provides one with all of the videos but this time he could not find it?

So bottom line is I am thinking I will use a 12AX7 as the 1st preamp, with the AA764 tone stack in between the 2 sections... then couple that into the grid of the 6SJ7 and have the volume control after the plate of the 6SJ7 before feeding into the 6L6. Can I get away with using a 12AT7 since I will have a 2nd preamp tube with the 6SJ7?

Thanks

Brian in NorCal.

[Reeltarded]

It looks FUN!

AT7 will be even less input gain, the second stage will make up some of that, but if you are shooting for clean and louder consider making V1 all about driving the tone section *next*. a TMB tone stack eats about 12 decibels. Fenders sound boomy and Marshalls sound carved. That mostly comes from where the stack is inserted.

[Stevem]

This comment might be short sighted, but how does one become a better guitar player when you leave your axe at a Cigar Lounge all week long?

I missed this the first time through this string.

[Brokegunner]

This comment might be short sighted, but how does one become a better guitar player when you leave your axe at a Cigar Lounge all week long?

I missed this the first time through this string.

At least he plays one a week... I'm trying to become an amp tech and let it sit on the shelf for 10 months