audio-talk

@Paul Barker Would it be possible to make the link available to the Youtube Video, where the info is supplied about the PMC Speaker being voiced to have similarity to the 57's.
As a long term 57 user and a Stacked 57 user for quite a few years, I made a few changes over the past few years, by ...

Have you referenced the heater to ground?

Maybe the se 6em7 should amplify to a phase splitter to a push pull driver to a push pull output stage. All multigrid indirectly heated triode connected valves. The EL38 fits the bill for the driver and the output stage. Whether the 6em7 soundstage continues through all that to the speakers is ...

Yes when it is on speakers the soundstage excels compared to dht’s which are hard to coax out of their veil.

I also found the Rosenblit original 6as7 OTL design filled the room from corner to corner.

I’m glad you could sense it on headphones.

Decided to RCR couple the output stage.

https://i.ibb.co/rjrj4sT/IMG-2737.jpg

Also double checked that px4, px25, 300b were not a better choice.


300b 4.4% thd
Px25 6% thd
Px4 3.1% thd

So the synergy of the 2a3 in the form of 6b4g matches best.

801a lower distortion but harder to fettle. I ...

Using the 625-0-625 tap, psud2 predicts 480v but I can’t show double 5R4 gyb (potato masher) so the voltage drop is less by 30v which means just plugged into the mains instead of the variac I get the voltage this project requires. However I dont want the Black Gates seeing the 570v start up for 0.3 ...

Just reviewing this amplifier, don’t worry its going ahead. But its a sobering thought that the cost of building for someone who hasn’t collected valve audio power transformers and chokes over many years, the cost of bespoke new transformers and chokes would be crippling.

Fortunately I bought a ...

https://i.ibb.co/pBCbzk6g/IMG-2727.jpg

Always forget to drawer the grid stoppers. 1k5 sufficient for all valve types in the circuit.

6b4g bias the 5k7 created 5k plus 700 ohm in series

300b 1k // 9k is perfect. But not available 10k is adequate makes a bias voltage difference of 1 v.

I’ve ...

OK managed to mount the original valve bases which the holes were punched for. Shame the transformer had to be mounted middle for diddle, didn't want a mounting leg interering with the stepped attenuator.
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https://i.postimg.cc/Qdk4n0Rd/IMG-0621.jpg

https://i.postimg.cc/8zVXHqXY/IMG-0622 ...

OK managed to mount the original valve bases which the holes were punched for. Shame the transformer had to be mounted middle for diddle, didn't want a mounting leg interering with the stepped attenuator.

I am very pleased with my left hand skills; doing tasks with it is how full recovery is ...

The stepped attenuator mounted the rca in and loudspeaker out’s are good quality and positioned well. Saves re-inventing the wheel to a blank tin Hammond box.

Now the obstacle to overcome is the front left mounting hole crowded underneath with the stepped attenuator.

The greatest clearance from the large interstage transformers is as pictured. Do we think this would work?
https://i.postimg.cc/DZB1n5Wc/IMG-0613.jpg

https://i.postimg.cc/2j9ntcNk/IMG ...

OK I have found a 2a3 (but substituded with 6b4g made in USA) an operating point pushing the dc current past 50mA to 54mA (the higher the current the lower the distortion) with the almost the same 2hd 3rd 4th and thd as the 300b output stage.

Paying attention to Nick’s point and Simon’s idea of ...

Yes Nick I looked at that with the 6b4g but the distortion was considerably more than the output stage.

So that, and the roll off in bass with inductance limitation not favoured, I looked at the srpp, then decided to make the srpp out of el36’s for heater simplicity; hoping the distortion is tamed ...

At last I have mounted which valve bases that I have. Had to order 8 different octal bases that I hope will fit the holes punched originally for Jumbo 4 Pin. Always loads of patience required for things to arive. But a mental victory that I began.

https://i.postimg.cc/j5t8hFQt/IMG-0612.jpg

The ...