Simple SE mods for 6DZ7s
6DZ7 - an interesting twin power pentode, with a potentially interesting application to the SSE board.
The 6DZ7 is an octal tube which contains the "guts" of two 6BQ5s (or 6GK6s).
Its pinout makes a paralleled 6DZ7 "somewhat" compatible with a 6L6 ,this can be configured for pseudo-triode or ultra-linear operation
This clearlys shows that a 6DZ7, with the control grids and plates paralleled can be used in an existing 6L6 SE circuit, with a few simple modifications:
Some simple mods to the Simple SE PC board, around the octal sockets would be required:
1: cut the etch connecting the output tube socket pins 1 and 8. (8 is the cathode, 1 will become a 6DZ7 G1 connection)
2: jumper pins 3 and 6 together (the two 6DZ7 plate pins)
The grid resistor for the paralleled 6DZ7 should be between 100K and 150K, in order to prevent unstable operation, as 270K is too high, and results in an unstable / drifting G1 voltage.
3: Jumper pins 1 and 5 together (G1 for each section) or better yet, add a second grid stopper resistor to pin 1, from the "top" of the grid resistor,this can be soldered to the bottom of the board.
4: The interstage coupling cap should be increased to 0.33 -0.47 uF / 600V
to compensate for the lower grid resistor.
5: use a 200 - 220 ohm, 5W cathode resistor for each octal socket, bypassed with 470 - 1000 uF, at least 35VDC rating.
6: The B+ voltage at the OPTs should be 365VDC, +/- 10 VDC.
This all will result in the equivalent of a parallel 6BQ5 / EL84 application for teh SSE board!
I've built up such a circuit point-to-point, and the next iteration will be translated to an SSE board.
/ed B in NC
They are somewhat scarce- I've ran across two in the last five or six years.
Two 12 watt tubes in parallel? Why not just use a 24 watt tube (i.e. 6L6GC) and save the 6DZ7's for a compact pp amp?
Seems like a solution in search of a problem.
But what the heck, I've slept on it - it might be kinda cool looking to see those two fat bottles on a Simple SE board ... tubes are no good unless you use them, so no point in saving them for the next guy, I say.
Let us know how the parallel tubes sound compared to a single.
I know I prefer the sound of the 2A3's that actually have two separate 45's in the bottle over the 2A3's that have a common plate.
My thought was that if you had to buy the 6DZ7's it wouldn't be worth it since you can get Chinese 6L6GC's for $3 to $5 each. Russian equivalents are cheap and sound reasonably good too.
They are so scarce, they are the only 6DZ7's I have seen. Wasn't there also a similar tube that had two 6L6 tubes in one bottle? 6DY7 maybe?
I guess when using these type tubes as a parallel tube combination, plate load would be one fourth the specification for normal push pull operation?
Both tubes are labled Stromberg Carlson. Both are used. One has obviously seen the red glow of death on one of the plates and its getter is nearly gone. I'll plug them in next time I have a Simple SE board in the hot seat.
My 6DZ7s are all GE manufactured, even though two of them are RCA branded. They have the definitive GE markings on them.
I lucked upon six NOS/NIB of these tubes at a NH hamradio swapfest several years ago, the seller must have thought that they were just some strange looking TV deflection tubes, so they went for dirt cheap. But then the same guy was selling NOS 12AX7s, 12AU7s and 12AT7s for 50 cents apiece. I'm definitely glad I was an "early bird" at that one. He was more interested in selling to the milirary surplus "boatanchor" radio crowd, and his tube prices reflected that...
I recently built up a PSE-UL stereo amp using two of these 6DZ7s, along with SRPP 6CG7 drivers.
Since 6DZ7s are basically "siamese twin" 6BQ5s sharing cathodes and screen grids, this was the obvious way to use then in UL mode. I "borrowed" the standard ST35 power supply design, with PA774 power trannie, but with additional capacitance (nearly 700 uF total) and used a C354 choke in place of the 50 ohm, 5W WW resistor. This thing definitely ROCKS! and sounds very good. OPTs are Edcor GXSE15-8-5Ks, and the 6CG7 SRPPs are run at 325V B+ and 5 mA. I could have squeezed another watt or two out of these by using GXSE15-8-3.5K OPTs but then I needed these for another oddball project using 6AV5GAs, and besides, the 5K OPTs give me lower 2HD and 3HD, a good trade off for a tad less watage.
This amp spawned another one, which uses 6GK6s in place of 6BQ5s, in a similar SE-UL design, but with one power tube per channel, and otherwise nearly identical, except for a smaller power trannie (Hammond 272BX). This gave me about 20VDC too much B+ voltage, but by using the 5V filament trannie to "buck" the primary voltage, it then delivered the correct B+.
/ed B in NC
At this point, I have other plans for the SSE board, which is already built up and ready to go, with two minor modificationms - I used yellow LEDs for the 12AT7 cathode resistors (for 1.873VDC on the cathode) and lowered the 10M45S CCS plate regulators to around 6mA (470 ohms rather than 330 ohms Iset resistor). Most of my previous experience with 12AT7s, I usually ran them around 3.5 mA, so I decided to try for a current level somehere in-between for this one.
I'm thinking of using a set of J/J 6V6S (which are pretty rugged tubes on theor own merit) in this and push them really hard... They can take some serious "abuse" in my PP Fender Deluxe clone guitar amp, so why not try it out in SE...
Like George says "Too much power is almost enough! Turn it up till it explodes - then back up just a little. "
I have 10 NOS GE's in my box bought from old tv repair shop for $1 ea .
Wondering if anyone has attempted paralleling the sections and wired in triode configuration. What could I expect for output wattage trioded?
If a el84 creates @ 2 watt trioded, could it be safe to guess about 4 watts?
I have a pair of James JS-6113HS's that may work with them trioded.
What do you think?
I'm guessing it should sound great.
I have breadboarded these wired push-pull and they were amazing.
Thanks in advance for Ideas and constructive critizism.
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