Amp No 46

[Nick]

I would assume it to ensure the transformer secondary is loaded, may help with ringing, or may help to specify a load as reflected into the primary and seen by the source.

Square waves and a scope would be how I would experiment with this. Will vary though with the position of the volume control as that will alter the load on the primary side.

It may be you can control ringing, but you may find you like the effect of the ringing.

[Nick]

The Sowter page specifies the frequency response with a 6k4 ohm source and 10k ohm load, but doesn't say what happens with other loads.

[Nick]

I would be tempted to use a pair of resistors to ground instead of a single one, would help with any grid current that occurs.

[Cressy Snr]

Cheers Nick,
I’ll have a look later for 4 resistors.

[Nick]

Then again, the DCR of the transformer will do just as good a job with grid current. Maybe ignore that.

[Cressy Snr]

OK.

[Cressy Snr]

I simply put 47K across the push pull pairs as Stephen did with his HPA project:

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[Cressy Snr]

Needed to put in a ground lift switch so that the RTZ and JDS Labs DACs could be used with the amp, otherwise there was an annoying buzz in the headphones.
The MF M1 DAC was no trouble with the primary of the IPT floating, but the other 2 DACs did not like the floating primary at all.

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[Cressy Snr]

I reverted the headphone amp to single ended operation last week, so it's now back to an ECC99 cascade.
Today I pimped up the casework with maroon Rexine because next to the turntable it looked like complete crap and was driving me nuts! Quite an involved job actually as I decided to take the raw DC supply for the Rod Coleman heater regulators off-board and replace the top plate with a bit of steel I had.

Spray contact adhesive is your friend when applying Rexine, I managed a flawless finish, both on the top plate and the front panel.

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The HPA looks very Dansette now.

[steve s]

Looks good Steve, lim quite envious as I don't seem to get time to do anything hobby wise nowadays

[Cressy Snr]

Here's the schematic.

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[Ant]

There is that red formica here if you want that, it will go straight over anything flat with some proper contact adhesive

[Cressy Snr]

There is that red formica here if you want that, it will go straight over anything flat with some proper contact adhesive

Yep, I'll have that for rebuilding the 1626 HPA.

[Cressy Snr]

Looks good Steve…

Thanks

[Paul Barker]

What a good job you had a pre II OPT!

You could also try the 45’s ? They should sound a lot better than the Darlings.

I also think the 6em 7’s sound much better than the Darlings. I can send you two if you dont have any. But doint use the first secction because they are poorly matched from one valve to another. Use your existing voltage amp.

I think the section 2 of 6EM7 is a wonderful sound. Its just not powerful enough for speakers unless they are over 100db.