ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

previous: Mike T Thanks Steve...nice page. What I'm... -- 1/19/1998 9:18 AM

Re: Unused Triode as Gain Stage

1/20/1998 5:24 PM
Craig	Re: Unused Triode as Gain Stage I've been trying the same type of experiments with my SF Champ. I ended up converting to a limited version of the BF Deluxe Reverb (AA763). I was pretty pleased with the results. Here's basically what I did: Everything is the same as the Deluxe throughout the power section, except filter cap values, and I went with a cathode bias - 500 ohms. I also omitted the vibrato and reverb. I went with the long-tail PI, with a 12AT7, and a GZ34 rectifier. I had an old Allied 10-watt output transformer, and it has a nice sound, so I dropped that in, making this amp something of a Champ/Princeton/Deluxe mutant. Actually, it's like a one channel, 10-watt BF Deluxe with no effects. (Probably more like 12 watts, if the A-B comparision I did with my housemate's Princeton Reverb is any gauge - mine is slightly louder). I also added a master volume, and a mid control. I'm still debating whether or not to yank the mid control, because I think I liked it better before, with the 6.8k to gnd. So the control panel resembles a Vibro-Champ. I tried a Mojo 10" as a replacement, but I had been prototyping using either a single or a pair of Jensen C12Q's and was really disappointed with the sound with the Mojo. So I built a Champ-12 style cab for one of the C12Q's. That was really fun, but without the proper dovetail jig, it was a bit less righteous. I added a small project box under the chassis to hold the filter caps, and used the original rect. socket for the added 6V6, and then used the filter cap hole to add another 8-pin socket for the GZ34 (Woo Hoo! same size!). Before I decided to add the cap housing, I found that I could neatly tuck the multi-cap sideways against the inside of the front panel, between the power switch and the Bass control pot. I used some double-sided, foam tape to secure it. I then added a pair of 10mmf caps in series to get an extra 20mmf. Worked out great, but then I changed it, because I wanted to free up the front panel for more mods later. I had to add a voltage divider between the 2nd preamp stage plate and the PI input, (47k/47k)to keep the gain down - I was running into trouble with the Champ power Xfrmr getting pretty hot after only a few minutes. Too much current. This solved the problem, but I'm not convinced it's the most elegant or best-sounding solution. I may give up on the Champ power tranny, and upgrade to the Deluxe, but I've been having fun trying to make it work, and I'm learning a lot. Anyway - thought you might be interested...the amp is really versatile; great distortion with the pre-gain at around 7 and master dimed. Great clean tones. The volume is still slightly less than adequate for rockin' out, but if I went with a Deluxe output transformer I could solve that. Let me know how your amp progresses. I'm interested in what you're doing. Craig

1/20/1998 5:24 PM

Craig

Re: Unused Triode as Gain Stage

I've been trying the same type of experiments with my SF Champ. I ended up converting to a limited version of the BF Deluxe Reverb (AA763). I was pretty pleased with the results. Here's basically what I did:

Everything is the same as the Deluxe throughout the power section, except filter cap values, and I went with a cathode bias - 500 ohms. I also omitted the vibrato and reverb. I went with the long-tail PI, with a 12AT7, and a GZ34 rectifier. I had an old Allied 10-watt output transformer, and it has a nice sound, so I dropped that in, making this amp something of a Champ/Princeton/Deluxe mutant.

Actually, it's like a one channel, 10-watt BF Deluxe with no effects. (Probably more like 12 watts, if the A-B comparision I did with my housemate's Princeton Reverb is any gauge - mine is slightly louder). I also added a master volume, and a mid control. I'm still debating whether or not to yank the mid control, because I think I liked it better before, with the 6.8k to gnd. So the control panel resembles a Vibro-Champ.

I tried a Mojo 10" as a replacement, but I had been prototyping using either a single or a pair of Jensen C12Q's and was really disappointed with the sound with the Mojo. So I built a Champ-12 style cab for one of the C12Q's. That was really fun, but without the proper dovetail jig, it was a bit less righteous.

I added a small project box under the chassis to hold the filter caps, and used the original rect. socket for the added 6V6, and then used the filter cap hole to add another 8-pin socket for the GZ34 (Woo Hoo! same size!). Before I decided to add the cap housing, I found that I could neatly tuck the multi-cap sideways against the inside of the front panel, between the power switch and the Bass control pot. I used some double-sided, foam tape to secure it. I then added a pair of 10mmf caps in series to get an extra 20mmf. Worked out great, but then I changed it, because I wanted to free up the front panel for more mods later.

I had to add a voltage divider between the 2nd preamp stage plate and the PI input, (47k/47k)to keep the gain down - I was running into trouble with the Champ power Xfrmr getting pretty hot after only a few minutes. Too much current. This solved the problem, but I'm not convinced it's the most elegant or best-sounding solution. I may give up on the Champ power tranny, and upgrade to the Deluxe, but I've been having fun trying to make it work, and I'm learning a lot.

Anyway - thought you might be interested...the amp is really versatile; great distortion with the pre-gain at around 7 and master dimed. Great clean tones. The volume is still slightly less than adequate for rockin' out, but if I went with a Deluxe output transformer I could solve that.

Let me know how your amp progresses. I'm interested in what you're doing.

Craig

Replies:

Mike T I used it last night at rehearsal, ... -- 1/22/1998 7:29 AM