I selected a power transformer that would produce between 300 and 305VDC based on mains voltage. I wanted to be able to run any EL84/6BQ5 in the amp. The EL84/6BQ5 has a maximum plate to cathode voltage of 300VDC. There is a super EL84/6BQ5 called the 7189 that can handle 400VDC cathode to plate. A lot of older 6BQ5s are actually re-labeled 7189s.
The amp biases up at around -11VDC, so the cathode to plate voltage is 289 to 294VDC. Lowering the plate voltage lowers the amp’s clean headroom, which when coupled with open-loop operation (no global feedback loop around the power section) results in harmonically rich, fat tone. I also have a toggle switch that removes the shared cathode resistor bypass capacitor in the power section. This mod makes the power section much more compressed.
Now, getting to the Soviet and Sino tubes. Well, the Soviet EL84/6BQ5 is not actually a real EL84/6BQ5. It is a tube with the designator 6P14P. The 6P14P has the original EL84/6BQ5 cathode to plate voltage rating of 300VDC. The Sovtek EL84M is a rugged version of the 6P14P with the designator 6P14P-EV. The 6P14P-EV is tough as nails, but is a very sterile sounding tube. The big amp companies like installing the 6P14P-EV because it allows them to get away with jacking up the plate voltage without having to worry about the power tube(s) failing while the amp is still under warranty. They can also get away with using an undersized power transformer that sags heavily under load. The power transfer that I used in my amp is capable of providing 167ma of current. At 305VDC, the amp draws around 100ma under heavy load; therefore, the bottom end does not farty like it does on amps like the Deluxe Reverb when the amp is pushed into overdrive. It sounds a lot like a mini-JMP Marshall 50W.
I run Tesla EL84s that I purchased the nineties in this amp that were made in the Tesla factory before it closed. The Tesla EL84 is a fat sounding EL84. JJ purchased the tooling from the Tesla factory, but they use a different filament.
You mention the Soviet tube designators and it reminds me of the small community that has developed around these mil-spec Soviet surplus tubes. I have seen some very interesting circuits over on the Watkins Amp forums (SEwatt.com, PPwatt.com, etc.) based on the 2 watt power pentodes (the 6P1P I believe) available from some of the sites like tubesstore.com.
What output transformer are you using with your 6BQ5s? A company by the name of ClassicTone makes a wonderful 15 watt OT I used to like for use with the EL84/6BQ5.
The company that manufacturers the ClassicTone transformers is Magnetic Components. Magnetic Components has been around forever, but they did not get into the guitar power and output transformer business until the 00s. I built this amp in 1997. I used a Hammond 125E universal output transformer. It was that output transformer or a Mojo Deluxe Reverb output transformer. I voiced the circuit to make the most of the iron. The amp violates all of the “expert” rules for building a tube-type guitar amplifier. I used metal film resistors, metalized polyester coupling caps, and solid copper 22-guage 300V hookup wire.
I only have one guitar which has any real value to a collector. Like others, mine collect dust and need to be played and by someone better than I am. I keep telling myself one day sooner or later I’m just going to have to do it.
Takamine Cedar Accoustic
First guitar I bought, love the sound, used money my grandmother gave me before she passed away. The bridge lifted and I had it worked on, but I’m not convinced he was the best luthier around even though he came highly recommended.
Yamaha Silent Guitar
I love this thing. 9V battery and earbuds and you are in business. Of course it is not truly silent, but you could get away with it most anywhere. Also it can be plugged in or ran through an amp.
Fender Starburst Mexican Stratocaster
Got this one and an amp for a song from a guy in CA. It was in fantastic shape, just dusty and needing new strings.
Fender Cherry Red Mexican Stratocaster
This one came out of GA by a supposed expert on guitars. It was packaged poorly and got dings on the way to me which really irritated the crap out of me. The pickguard was not even right on the guitar it was for another model. Love the looks of this one.
Fender Starburst American Stratocaster Roland Modeling Guitar (VG-8)
This is the one which has some value. It can model 37 different Stratocaster, Telecaster, humbucking, 12-string and acoustic sounds, plus five alternate tunings, all at the simple flip of a switch or twist of a knob. (I copied that verbiage.) It used batteries for the modeling and burned them up quick. People complained it would not make it through a session. The parts for the battery were nearly impossible to find so I just removed the batteries and put it back in the case. A few years ago I spotted a power supply, but it was only available with a new less expensive Modeling Strat or from overseas. I put it in backorder from a NY store and finally after about 18 months they said it could not be found. I did another internet search and found one and so now I have the option of batteries or the power supply to use the guitar. It is a great guitar and at one time I could have told you how old it was.
The most interesting, and only one of them likely to be collectable, is my 1983 Steinberger XL-2 “boat oar” bass - serial number 563. I bought it new and have been the only owner. It’s the version with EMS humbuckers and the curved bayonet “plug-in” leg rest (which somehow I’ve managed not to lose through the years). The original gig bag bit the dust a few years ago after lots of wear and tear from gigging, so not I keep it in a custom road case. I don’t get to play it a lot, but I don’t think I’ll ever let it go. I’ll probably pass it on to my son who also plays.
I also have a Mexican Fender P-bass. I’ve made a few cosmetic mods to it, but it’s pretty much “stock.”
I’ve always run my basses direct to the sound board through an Intersound IVP preamp/DI combo - so I don’t even own a bass rig anymore.
I have a Larrivee D-03R acoustic that I like a lot and play the most. It’s a dreadnaught with rosewood sides & back and solid sitka spruce top. The neck is mahogany with ebony fretboard. I added a Fishman passive piezo pickup and run that through an external Fishman preamp.
The last is a Mexican Fender Telecaster that I’ve made some mods to. I swapped-out the pickguard for cosmetic reasons and added some shielding in the cavity when I did that. I’m planning to swap out the factory pickups for the NS-2 noiseless ones. I keep the pedals pretty minimal - overdrive, chorus, flanger, compressor, delay. My amp is a Fender Blues Junior NOS.
I don’t know much about guitars either. I have my dad’s old 12 string Martin which looks an awful lot like this:
I think it’s a late 60’s model, but will have to figure that out.
At one point I got to the point where I could play a few chords and bought a cheaper 6 string acoustic (which was a little more forgiving than the 12). One of these days when I don’t have 3 kids running around the house I’d love to carve out some time and pick this back up.
Yeah, the action is really low and smooth, and it sounds great. Its one with the maple neck. I verified that it is MIJ, 92 or 93 based on the serial number.
Love playing it, just don’t do it much any more. Great bang for the buck, IMO.