Monday, November 4, 2013

"Abstinence" - 6EM7 power amplifier

Yet another 6EM7 power amplifier. This time some expensive and different parts were use in construction and a different internal layout was employed. The power transformer and choke are isolated top and bottom by rubber grommets. This ensures no AC vibration reaches the tubes.The initial PS filtering is preceded with a on-board power filter, a 4uf\400V Russian PIO cap and 20H\100mA Hammond choke. The HT is supplied by a Hammond power transformer and a very expensive Sophia Electric mesh plate rectifier tube. The second stage of filtering is 47uf and 100uf electros. with a large limiting resistor ensure the amp is totally free from of hum and noise. All PS caps and cathode bypass caps are snubbed.

This amp sounds better than the last and I think it may be the Sylvania NOS 6EM7 tubes. Russian Teflon caps are used in the inter-stage coupling  and once more large NP caps for the bypass on the power tubes. For the first time I have used Chinese made H&K 15W OPTs, can't fault them. The look of the amp is almost under-stated "sexy" and the sound the same - sexy and natural.


Astrozon said...

Nice! The 6EM7 (and 13EM7) are starting to get better known as great sounding power tubes. They were common in the 50s, but somehow didn't get found again until around 5 years ago. Great looking amp!

retro-thermionic said...

Sorry, a little late with my comment but thanks for the nice remarks. I've just done some real serious upgrades to the amp:

I decided to pimp Abstinence:

1 - Remove 22uf electros as first cap in PS and replace with 4uf\400V Russian PIO and snub with 0.1uf\630V poly
2 - Place to 100ohm\5W resistors between power tranni and rec. tube plates (control surge)
3 - Reduce last filtering\limiting R in PS to compensate for 100ohms on plates
4 - Replace orange drops with Russian Teflon 0.033uf\400V inter-stage caps
5 - Snub 100uf NP bypass caps (Ck) with 0.1uf polies.
6 - Replace the $24 5Y3 rec. tube with the $200 Sophia Electric mesh plate.
7 - Added sound deadening (bitumised Al) to bottom plate

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