“ZeroOne-A” - 100 year old globe DHT tubes preamp.

 

Inspired by my 71a tube amp I thought I would try another DHT preamp but with a 01a tube. Again Cunningham tubes used as with the 71a but with the 71a I also have RCA tubes. These globes are from the mid 1920s. Where the 71a preamp - “MWH” - has mainly carbon film resistors in the signal path and a Russian PIO output cap this build has all metal film resistors and a Mundorf EVO oil output cap. 

To enhance the performance of both preamps I built a new much beefier external PS on a repurposed cast AL chassis which already had a RFI/EMI power filter added. The 5V DC on the heaters is regulated and balanced. The 01a preamp has a remote Alps volume control and two inputs. Hookup wiring is via fine silver plated copper wire and high quality heavy duty RCAs ate  used. Not a lot of gain but a very revealing, detailed sound with extended reverb. Love the colour - Iron Stone.

A 6N7 preamp with remote

The now converted 01a preamp is now a RCA - NOS NIB - 6N7. The tube is metal (No!) so not much of a glow and is a dual triode with single cathode. The tubes are wired as a single triode with grids and plates paralleled. 
 

This preamp was designed for me many years back and was originally built into a timber box as “Heavy Metal”. It had heat issues. In the better and classier chassis looks retro and business like. With Alps Blue Velvet remote pot. 
 

I required 0.68uf output caps but had none of that value. But did have four 0.33uf Sprague orange drops. Doubled them up for a near enough 0.66uf. Had them for decades, as the tubes, so time to use them. Most 1W carbon film resistors and some metal film and wire wound. Double Pi HT filtration - 300uf total. 
 

DC on heaters, 260V HT and 2.55V bias. All on point. Gain should be 20db with Rk un-bypassed. 

 

Tubes are run in but the rest new so some complete burn in time required. Sounding relaxed and midrangy with voice a standout from the sound stage. Dead quiet operation with retro-Zen EL34 amp but hummed with my latest EL34 amp. Very happy so far. 

“Perspective” - EL34 Single End Ultra-linear power amp

 

This amp is based on a pair of new Mullard reissue matched EL34s with a universal driver tube. Any 12A*7 can be used as a driver. OPTs are Asian 3.5K 10W with 4 and 8 ohm taps. I have used the 5W 5K versions in other amps with outstanding results. The OPTs and power trannies are shock mounted on split rubber grommets to reduce resonance.  The PS is external with over specced Hammond power tranni. A Sylvania 5U4GB handles rectification. 357uf of filter caps smooth and store 366V of HT. Further filtering feeds the driver tube with a 4uf PIO cap and 2.5K 2W resistor. The amp is very, very quiet. 

Filament current is rectified with a 10A bridge and single Pi filtering - 9400uf of filtration. HT and filament caps are snubbed with 0.1uf polies to reduce noise. The chassis is a Hammond wood cheek and is made of steel for strength. The finish is black stipple. The chassis for the PS is cast Al with a black epoxy enamel finish. The PS is fused and earthed. 

RCAs are Paladium plated and speaker posts solid brass with gold plate. Audio path wiring is fine silver plated copper wire. All wiring is point-2-point, no cct. brds. and no shielded wire. Not required. Sockets are ceramic and power is brought to the amp via three pin large XLR connection. The driver tube being used here is a Tung-Sol ECC803S gold pin. 6L6 and KT88 can be rolled here and any 12AX7 equiv. can also be rolled. 

Amp presents full bass and a complex warm soundstage with smooth highs. It is a pure Class A amp. Not only good looking but excellent sounding and definitely worth the weeks of work. The EL34s I’ve had for twenty years so now they get to entertain as they are designed to do. 

“retro-Zen” Decware inspired 6BQ5/EL84 triode strapped amp

 

A Decware inspired 6BQ5/EL84 (Zen) triode strapped amp with attenuator. Driver is 6N1P. And of course chicken beak knob with AWV 6BQ5.

OPTs are 5W Asian sourced which I and others have used and find excellent. They are shock mounted on split rubber grommets for HF/resonance suppression. Sockets are ceramic and gold plated with Visheys MKP interstage caps. Hookup wire is Cat5 solid core. 

External PS has a Sylvania 5U4GB and works with two other power amps saving me $400 each amp. But if I sell one ill have to make another PS. Power tranni is Hammond. Chassis is a cast Al with Epoxy Enamel paint. This is meant to be a fun amp, single input and just 2.5W. Good den amp or desktop amp. For good level music listening you need speakers with better the 90db sensitivity.

“Hegemony” - 6L6 monoblocks.

 

I was asked to build 6L6 monoblocks for a very keen tube collector. He would provide the tubes and I would build the amps. Monoblocks are almost double the work with two power trannies and filtering circuits. The requirements were also to use Silk OPTs from Thailand. I chose 20W models for a 5W amp. Interstage caps are Mundorf Evo oils. RCAs are Palladium.

These austere looking smart amps produce deep articulated bass, grounded detailed and rich midrange and crisp highs. Chassis are Hammond steel with wood cheeks and are difficult to drill but worth the effort. Hammond power trannies and 300uf of filtering in a double Pi config produce a very low noise (1.5mV) amp which plays plenty loud. Definitely one of my better and more expensive builds. You are rewarded, though, with an exceptional audio experience. 

“Rhetoric” - EAR834p MM phono stage

EAR834p MM phono stage in a Hammond wood cheek. External PS with Hammond tranni. DC on the heaters and the HT is electronically smoothed. Palladium and copper RCAs, and fine copper silver plated hookup wire. Im not supplying tubes but here Ratheon 12AU7 and two Mullard 12AX7 re-issues. 

“Elements” - 12AX7 SRPP preamp with remote

 

Built mainly from parts on hand including tubes (Gold Lion), enclosures, output caps and power tranni. The power tranni I got free because the filament windings were open. I had a 12V tranni on hand and was used here for heater voltage. 

Three inputs and Alps remote volume control with RFI/EMI filter in the external PS. Russian military metal clad output caps in a Hammond extruded anodised Al enclosure with a big gold knob make this a smart looking build. Brilliant sounding as well as smart looking, a great use for so many parts which had remained unused.