16GK6 PP amp

[paul1973]

Hello to you all,

This is my first post here. I was reading all threads from this great forum for almost two years and I thought it might be time to show you my PP amp project. The inspiration came from the compactron ST35 build from Terry Smith. I love oddball tubes and sleepers and since I 've bought a box of about eighty Philips NOS 16GK6 tubes on the bay it was the logical thing to construct some nice amplifier around them. It is not a ST35 clone since I dont like the idea of running my tubes significantly above the recommended ratings (no offence, I realy like the Dynaco). Besides that I really do not need 17 watt stereo rms. I've used a very simple schematic for a 12AX7 as a driver in floating parafrase for phase splitting.



Oddball powertubes needs a oddball driver and therefore I bought a pair of 20EZ7 double triodes. Just a 12AX7 with a scrambled pinout and a 20 volts, 100mA filament.

The power transformer you see is an old Siemens transformer from professional equipment. It has four filament windings and some of them are centertapped. A 16 volts filament line was easy to come by. The 20EZ7's are getting DC to avoid 50hz hum problems. Outputtransformers are Hammond 1650F.



On the moment I'm still wiring and soldering. No music yet. But it will take just a couple of evenings.

Next project wil be a full compactron amp with 6AY11 (12AX7 plus two diodes) and 6JB5. The latter can be compared with a 6V6GT. You do not find Compactrons at a garage sale in The Netherlands (TV tech was very continent specific) but Ebay is a great help.

Updates will soon follow,

Regards,

Paul

[TomMcNally]

Nice looking amp Paul!
Let us know how it sounds when you get it fired up.

... tom

[mesherm]

Nice looking amp. Excellent use of plinker tubes!
Keep them coming.
Mike

[paul1973]

Thanks for the compliments. It's almost ready to be fired up. Buzzy doing the wiring I learned that de 20EZ7 has a center tapped filament for 10 volts, 200 mA operation. That should be an ideal combination with a quad of 10GK6's or 10BQ5's. To late for me to rewire. Besides that, it works fine on 20 volts DC.

Paul

[paul1973]

It works! After a short 'debugging' surgery the amp is playing well. I gives a great sound. Powerful, strong, clear and… loud. I never knew that 2 x 12 watts so powerful. That’s all I have to say about the sound. Words are too weak for an exact description of sound. Kind of like describing a love scene in a novel: you have to be in it to really get it.

Regards,

Paul

[TerrySmith]

Lookin good! Those tubes are basically the equivalent of NOS EL84 and 12AX7 tubes at a fraction of the price!

[paul1973]

Lookin good! Those tubes are basically the equivalent of NOS EL84 and 12AX7 tubes at a fraction of the price!

More than equivalent: they're completely identical in construction. On the picture you see a 16GK6 tube next to an 6BQ5/EL84. Both are from Philips. I believe that they were branded Amperex in the USA. They are sounding the same to.

[EWBrown]

Amperex is Philips' other "export" name. Also they used the brand name "Norelco" (Northern Electric Co)

20EZ7 is a 6EU7 with a 20V filament. The "odd" pinout of these tubes was done for reducing the potential for any AC hum problems, as the filament pins are more separate from the grids than with the 12AX7 or other 9A / 9AJ pinouts. IIRC a lot of jukeboxes (at least Seeburgs) used 6EU7s in their gain stages.

Many of the 20V filament triodes like 20EZ7 and the WE407A, which has a 40V/20V CT filament were used in telephone "in-line" repeaters, which took their DC power from the multiplexers at each end of the line, each repeater consumed approx 200VDC (for both B+ and filament voltages) and these were connected in series, much like the old fashioned Christmas tree lights. These repeaters looked like a fat cylinder about 20-24 inches long, spaced at the required intervals necessary to overcome the line losses.

Each end terminal unit could deliver up to 2,000VDC, current-regulated, to feed power to the line, in either positive or negative voltage, in relation to ground. Which meant that the carrier cables or "open wires" could have a lethally high DCvoltage on them, inaddition to the relatievly low signal voltages. There could be up to a 4KV DC differential between the two end units

These repeaters also had a built in "fail-safe" mode, in which a bad or "dead" repeater would shunt itself out of the circuit, bypassing itself with relays. the overall gain was reduced, but the signals still could get through..

I worked on some of this (analog FDM 24 channel carrier) stuff way back when, about 40 years ago. Some of this gear, couild carry a voice channel and a 1200/2200 Hz telegraph channel on each of the 24 individual channels, as well as various control tone signals (like 1600 Hz for activating the ring generators). And, all of that without a single transistor or integrated circuit

FWIW, 6BQ5 also has an 8V and 10V filament version, and the 16GK6 also has 6V, 10V, 29V and (supposedly) 45V filament versions.

/ed B

[paul1973]

Wow! I'am starting to understand why Western Electric had a reputation for rugged durable tubes.