Anybody build a BFDR w/no reverb or trem single channel?

[ron vogel]

I'm considering changing my 6G2 build into this. All I want is a simple amp with just a BMT tone control and a volume knob. My PT is a 330-0-330 which should get me the voltage I need no problem with a 5V4...with a 5Y3 in the 6G2 circuit I'm right about 390V.

Any insight?

[Chuck H]

One consideration that needs to be addressed is the peripheral loading of the signal that results from the "other" channel, the reverb circuit and the trem. If you don't account for these the amp will have a lot more gain than an actual BF type amp. For better or worse depending on how you look at it. On the one hand you have more ability to clip the circuit. On the other hand it becomes impossible to nail stock BF tones because the gain structure doesn't mate up with other circuit parameters the same way. It's not quite as simple as just turning down the volume knob. I've built amps that approach the design you propose and found that just stripping out the parts of the circuit you don't want doesn't work as you might expect. Some of the signal loading caused by the omitted peripheral circuits needs to be accounted for. Just adding gain to a BFish preamp can result in a flabby overdrive sound because of the big mid scoop and extra bass capability of the BF tonestack. If you like the extra gain you'd need to adjust frequency to get out of the mud, but then you lose the clean tones. If you design out the extra gain you're pretty much just playing through the "normal" BF channel, which is pretty much a clean tone one trick pony and ends up seeming anemic in short order. That's why those amps had reverb and trem! I think most players automatically plug into the reverb channel on BF amps. You can tell when you look at the old ones because there's virtually no wear and scratches on the normal channel jack My solution was extra switches to allow adjustment between stock-ish and hot rodded circuits to add more versatility, but then it's not the simple, clean design you're probably envisioning for the project. JM2C

[ron vogel]

Pretty much why I think I'm going to have to use cathode bias, and the BMT stack should help bring it down a bit. The 6G2 I have it set up for now has way too much gain for me...and it's not nice to power tubes either....especially with the trem on. I'm wondering now If it may be best to parallel the 12ax7 input and put the tone stack behind it, then go with a 12ax7 for the PI instead of the 12at7.

[ron vogel]

Another option is to do what Leo did, and not have a cap on the resistor for the bias in V1B like in the 6G2...I put one in and experimented a little. It's still in there, but I had to do major futzing with the PI for it to play nice. Right now the amp sounds very good...but it's not quite right, and with the changes I made to sculpt the tone and gain made the trem buggy. It works, but not like it should.

[pdf64]

As per Chuck's thought's, consider inserting a master volume prior to the phase splitter, even if just a preset trimmer type, or a fixed resistor potential divider, reducing the signal level to ~ 1/4; suggest a 100k or 220k pot.
Bear in mind that the 50k trem intensity pot of the regular circuit presents a significant load on the preceding stage, maybe halving the signal level, then it's halved again by the 220k mixers.

[ron vogel]

As per Chuck's thought's, consider inserting a master volume prior to the phase splitter, even if just a preset trimmer type, or a fixed resistor potential divider, reducing the signal level to ~ 1/4; suggest a 100k or 220k pot.
Bear in mind that the 50k trem intensity pot of the regular circuit presents a significant load on the preceding stage, maybe halving the signal level, then it's halved again by the 220k mixers.

Yeah, I can see why a MV would be nice. Also, I realize a fixed bias would be better...well optimal for efficiency. However, I'm switching over to ceramic from alnico. I'd like to retain the compression from the speaker, but build it into the circuit. It'll help pull a little volume down...and that's a good thing in my situation. Trying to tighten up the bass a little with the ceramic, but I don't want the punch and icepick.

[ron vogel]

Ooooh, just looked at that closer. I was planning on doing a pull switch on the treble for a bright switch already. I could do a pull boost on the volume instead of a MV. Maybe a 56K to ground, and toy with a lower resistance for the boost. Nice!

[Chuck H]

If you like a simple control panel and stealth switching options you'll have a lot of fun. Sounds like you already are.

[ron vogel]

Hey, I didn't even know they made a non-reverb blackface deluxe until I posted this thread and started looking. Guessing they weren't all that popular?

[Chuck H]

There's a few out there. I see them now and then in the hands of someone less than a collector who thinks they really have something collectible