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I've got a Bogen "Challenge"

Ok thanks. I got them in a box of stuff I bought from a guy having a garage sale. Two are absolutely brand spankin NOS. I'll see what happens when I fix it. Thanks again man.
 
Ok boys! I truly don't know what possessed me to do this today, I'm in the middle of two Maggie builds and waiting for parts for my x-101-C. BUT. I opened up the Bogen today. First I set the gain MUCH lower on the 6J5. Added a grid stopper. Worked! But. Had some hissing, which I don't remember it having before. At all. It was a good step though so I continued. Neatebed up a bunch of sloppy work, redid some grounds, fixed the horrible way I jumped the heater wiring. Next step was to tweak the feedback resistor. That landed on 82k. Sounded right to me. Still had some hiss though, hiss that is constant, doesn't change with volume. When the music is playing you can't hear it. I went back and checked out the schematic, where it sounded best before, the deep bass setting, there was a 2200 pf cap that bypassed the NFB resistor. The only silver mica cap I had was 220, so I tacked it in. The hiss is ALMOST gone, and the music sounds fantastic. I'm not sure what, if anything, I'll do about the hiss but I'm totally stoked that I figured some stuff out and it sounds good!! Any suggestions as to what the hiss could be? It's possible (likely as I recall) that I really toasted the volume pot way back when, could that contribute?
Anyway, I just wanted to check in with you guys. I'm happy. Now it goes to the back burner again but GOOD.
Oh, still just slightly microphonic, but as long as I'm not tapping on the chassis, it's all good. Short of isolating that 6j5 socket I don't know what I can do about that. Later! Woohoo!
 
I found some hiss in a loose input jack and RCA cables... VC may play into it also... Some metal can tubes can be grounded thru pin 1... I find it helps noise suppression if its grounded...
 
Yes sir, I did ground that as you instructed. Thanks for that. Input wiring should be all good. VC?
 
Had a feeling. Next time I'm in there I'll swap them out. I'm already back in a Maggie....
Thanks Bill
 
Sorry to bring this thread back from the dead but I bought a CH-18 a little while ago and I’ve been working on converting to guitar. Please bear in mind I am a novice and this is my first project. Can anyone comment on the input section? The grid leak resistor is 1M on the first 6SF5. All I’ve read on grid leak bias talk about using 5–10M. Is this because the 6SF5 is high gain? Can a 5M be used?

Would the input benefit from a grid stopper say around 33K to reduce high frequency noise?

Is the input impedance high enough for guitar? There is no 1M input resistor but does the grid leak resistor achieve the same thing?

So far Ive put in 1/4 inch input and speaker jacks. Replaced wax caps and ecaps. Removed the negative feedback going to the 6V6 cathodes. Changed volume pot to 1M and put in a 1M tone pot instead of the phono volume. 0.047uF tone cap and 470pF bright cap wired like a 5E3 tone/volume

Thx!
 
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Duce67us said:
Here is mine.
I didn't plan on putting it out there for display either, but It might help someone down the road.

I was more interested in the "Guts" than the cosmetics. :) View attachment 748611 View attachment 748609
Click to expand...
i have done a few of those....Since I am probably no better than the average tube tech....I'll give you a great cosmetic tip...don't remove those goofy 5 pin jacks in the rear. Instead you can drill a 1\4" hole right through he center of them and put your 1\4" jacks right through them. Looks much better than the goofy washers and spacers I have seen some use. They are built very well indeed.
 
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