Wednesday, April 30, 2008

On Top Of Ol' Smoky


One night, Stephen Schneider (mentioned previously, referred to as SS here, the rest of the way out) brought out one of his Bell Sound P.A. amplifiers to our H.O.O.T. (also mentioned before now) meeting and showed us just what a marvelously toneful harp amp it was. Of course, we were listening to his masterful playing that was an important element to that tone, but when each of us had a chance to blow through its vintage tubes and it made most of us sound a little better for it, then it was apparent that this amp had quite of bit of merit. The Bell really had a whomping bottom end as good as anything I'd ever heard and just the right amount of compressed distortion. He bought the one he had off of ebay for a darned reasonable price, so I thought that I would keep my eye out for such an amp whenever I was surfing the auction site.

Not many months later (Summer of 2004), I saw a similar amplifier up for bid for $2 and the ending time was later that night. So, I figured that I'd toss out $2.25 for my bid before I went to bed. I woke to an e-mail proclaiming, "Congratulations, You Won!". Oh, wow! I really wasn't prepared for that statement. Yeah, I had looked at the pictures that showed an amp that had quite a bit of surface rust and no claims that the amp was in working condition, but I still expected someone to snipe in for more than $2.25. But, no, it was mine now. Pretty sure that these types of amplifiers have gained the nickname of boatanchors due to their bulk and weight, because it cost me ten time more to ship the amp to Texas than the price of the bid. Still seemed like a heck of a deal.

This particular amp model turned out to be a Bell Sound 3725A amplifier (circa 1939), which differed from SS's 3725B in several ways; one being that his runs two 6V6 power tubes and the "A" runs on two 6L6 s and mine was dead on arrival and lived up to the boatanchor tag because it looked as if it was fished up from the bottom of a lake. It was one rusted looking hunk of junk, especially the bottom half that apparently spent some kind of time exposed to water. When I pulled the bottom plate off to check out the inner guts, it crumbled in my hands. What I spied inside, was the apparent result of a fire melting wiring, capacitors, and resistors and charring the interior--it was dubbed "Ol' Smoky" from that point forward. I kind of enjoyed the challenge of working on the Silvertone, but this look way beyond a challenge.

I e-mailed SS that since he had gotten me into this amp stuff, that he was in for it on this one. I had already downloaded a SAMS photofact schematic and placed an order for two new 6L6s along with a 5U4 rectifier tube, a 6N7, 6SF5, and two 7B7 tubes before the amplifier's arrival, in anticipation of needing them immediately or later down the road. I went to work scraping crud that had built up just about everywhere and then ran the suggested voltage tests and such from the SS advisory board.

After replacing new tubes, burnt wiring, resistors and capacitors, I changed out the speaker and input jacks to the more modern 1/4 style to see what kind of sound I could get out of this monster after I plugged into my speaker cab. Zilch, nada, nothing, not even a blip came forth. SS would toss out ideas involving the resistance or capacitance in the signal chain and still nothing. I replaced the filter caps and then went to work just yanking and replacing and hacking. Still nothing and there wasn't a heck of lot left to replace--THEN. This amplifier could run either a 6SL7 or a 6SF5 tube in one of the sockets and the new tube that I put in was a 6SF5 and it wasn't until I checked a tube pinout diagram that I realized that they were meant for two different wiring scenarios. I stuck the 6SL7 in and VOILA! Instant sound, that sounded pretty darned good. So, I most likely could have stopped my soldering practice at any point in the refurbishing process if it had not been for my rookie mistake. The resistors that didn't need replacing might have made for a sweeter vintage sound. Oh, well. I learn a bit more than I knew before I began and that is what I tell my students that education is all about.

From there, we went to tweaking and experimenting with different rectifiers and power tubes and zenered the thing down to harp friendly voltages, and it makes a fine amplifier for $2.25 plus shipping. Not as good as the SS version for harp and not as good as the 1483, but not too darned bad either. Anyway--
Update--READ the comments because SS chimes in and adds some corrections regarding the Bell 3725B amplifer and others that he owns and is the reason for all this stuff in the first place. Glad he's around to keep me straight.

5 comments:

Mike Lynch said...

Gawd, I just love amp porn!

Ricky Bush said...

Yeah, this sucker was something to behold in its original state. It'll be one that doesn't find its way out of the house very often, but it's fun to blast around the house with.
See ya-
Rick

HTownFess said...

Hey Rick, my two 3725Bs are both 6L6 amps, it's that little blue 3710P 10w 2x10 that's a 6V6 amp. The 3715 model is a two-channel 6V6 circuit in the same casing as the 3725, with a 3725-style preamp circuit. Wouldn't mind having one.

My 3725Bs are relatively stock, just set up so the input plate voltage can be switched from 150v for harp/vocals to 180-220v for blues guitar use. I usually put in a 5R4 for harp use with a 4x10 cab, but the stock 5U4 or even a tighter GZ34 for vocal use--were you there the time Madcat Ruth used my Bell rig as the PA for a seminar? Any decent 6L6 or 5881 sounds good in a 3725, like the SEDs for harp and JJs for max output on vocals.

One of my 3725s is waiting for major filter cap modernization--I am going to try some heavier filtering in front to tighten up the lows for harp and get a tighter note envelope for vocals/acoustic guitar at the same time. It will probably be more like a 30-35w amp with a GZ34. I'd swear that anchor of yours is more like 30+ watts when not zenered.

Really fine amps, on the short list of coolest-looking PA heads ever, particularly the 3725B model. Harlem Slim called my first 3725B "just about the pinnacle of U.S. industrial design" the first time he saw it. Tony Vega just stared at it like Nipper the RCA dog.

Ricky Bush said...

Thanks, 'Fess. It's great to have you around to keep me straight, because the ol' memory card is too full when I'm posting sometimes.

Anonymous said...

If anyone is looking for one of these I just listed a Bell 3725A amp on eBay today (July 30th). It's really clean and powers up. Thanks, feec