Building the Push Pull Parallel Triode Amps

Push Pull Parallel Triode 6L6 / EL34

Mono Amps using ElectraPrint OPT and Hammond Power Transformer

Pete Millet's Universal "UNIAMP" boards from 2001 with Sowter 3575c input transformers used for signal splitting.  Pete's Universal Driver Board  Note that the schematic for these boards calls for a 100 ohm resistor for decoupling the power supply sections, which was way too small to prevent oscillations.  Changed to 1000 ohms.

Originally this amp had custom current sink bias set to 47mA each tube.  This did work and sound good, however, regulating 100mA per board required larger heatsinks than were used.  To get the right size heat sinks would require a lot of rework to the chassis.  Instead, these amps were converted to using the TentLabs autobias modules.  These modules set a current draw and vary the negative bias at the grid to match the bias.  This system fit into the chassis and works very good, better than the original current sinks.

TentLabs Bias Supply

 From Tube Cad Journal:   https://tubecad.com/2021/03/blog0531.htm

Output tube bias from cathode bias with the TCJ Harder Still circuit using 8 of these circuits.

PP KT88 Triode

PP KT88 Triode

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LL1660S/AM/PP 

Lundahl Amorphous Core Transformer Phase Splitter

Now all Lundahl

With surplus Output Transformers

Much tweaking to get the final product.
6V6GT phase splitter driver replaced with 6SN7GT

Lundahl Phase Splitter Transformer w/ Amorphous Core

No power supply electrolytics (only 2 electrolytic cathode bypass caps)

Amphenol MilSpec Power Connectors

Neutrik Speakon & PowerCon

Started with different phase splitter transformers

Bias/VU Meter

Solen 100uf Metal Can films. Dual Mono power supply.

 

Heathkit AA-32- Archeology

 

The Heathkit AA-32

Good ol' Ebay

About 20 years ago I bought a sealed Heathkit AA-23 for about $200 and stuck it in a closet.  I felt an affinity to it because at that time I was working in a building Benton Harbor, MI that some of the Heathkit operations had used.  The last copyright date on the materials I could find was 1969.

Huge respect for people back then that could assemble this as a beginner with limited experience.  Society must have been better and more practical back in the day.

When I opened it everything looked brand new.

I replaced the electrolytic caps with modern equivalents.

The tubes are what you would expect from a 1960's budget kit amp, 6EU7s and the venerable 6GW8/ECL86 combo output tube.

The next pictures show the buid-up of the parts.  I have been building things for quite a while and this thing was a challenge. Part of it was the 34 page step by step instructions with non-intuitive 

"Connect a 4-1/2" wire from lug 1 of terminal strip D (S-3) to lug 1 of terminal strip E (S-2)" 

Looking up pictures of which terminal strip/lugs etc was headache inducing.  Ended up with just using the pictures and the schematic.

I uprated the voltage doubler from the supplied 30uf caps to 200uf caps and UF rectifier diodes.  I also used the Sprague Orange Drop 716p instead of the supplied caps as they looked rather powdery.  I also added a 100uf cap at the end of the chain to keep everything quiet.  The amp has virtually no hum despite the tiny 1" shallow chassis.  Full phono stage and bass/treble controls too.  It sounds like an amp, decent highs and bass for its 8 watt output.  

(One of the 6GW8 tubes did not survive hibernation so waiting on a replacement.)

With potentiometer upgrade.  The original volume control was all over the place channel to channel.

A build based on Metasonix TX-1 guitar noisemaker with a
SE 6V6 output

It has a life of its own.
 

Maximum 300b (KR 842 VHD)

Pete Millet A2 Driver

Rod Coleman filament supplies

Buddha Camille Constant Current Source

Camille Cascode Constant Current Source (C4S) on the 6SL7

Three Toroidal Transformers 

Four Chokes

MOSFET B+ Regulators

Amphenol Umbilical Connectors

 

304tl - Finished!!!

Finished - Eimac 304tl Single Ended Mono Amps

They have a certain appeal

Construction was as modular as possible

Safety is critical in these amps as there is 1,100 volts on the heat dissipating plate cap

They also put out considerable heat.  Like sitting by a fireplace!

Stereo 6550 - The Dorm Amp

Building an SE 6550 amp with my Daughter

The little Output Transformers just would not do.  These are the full sized Edcors.  Now we have Bass

 Edcor 10 watt SE OPTs are fine as this amp is not asked to perform bass duties

Currently used to drive Klipsch Heresy speakers 80Hz and above.
Low end handled by a NAD2200 and a 12 inch passive subwoofer

It can provide a very high output