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-   -   FS: Vintage 1960s homebuilt Dual-Mono Mullard 5-20 amp (EL34/Acrosound TO-300 OPTs) (https://www.diyaudio.com/forums/swap-meet/324280-fs-vintage-1960s-homebuilt-dual-mono-mullard-5-20-amp-el34-acrosound-300-opts.html)

GordonW 24th June 2018 05:16 PM

FS: Vintage 1960s homebuilt Dual-Mono Mullard 5-20 amp (EL34/Acrosound TO-300 OPTs)
 
10 Attachment(s)
This amp is pretty special.

https://www.diyaudio.com/forums/atta...4-jpg-jpeg-jpg

It's a classic Mullard 5-20 design, built in the 1960s. It's done pretty much by the book, except for a few upgrades which allow more precise calibration, and it has some exceptionally excellent parts choices.

https://www.diyaudio.com/forums/atta...5-jpg-jpeg-jpg

Here's the main features:
- Dual-mono construction (two of everything- transformers, chokes, etc)
- Everything built in mirror image, in both power supply chassis and output chassis
- Oil-filled power supply caps
- Output chassis is aluminum (hum and noise reduction compared to steel)
- Preamp/driver circuitry done on tag boards (very professional)
- All grounds on central bus (basically star grounded)
- Input gain pots
- AC balance pots on phase inverters
- DC balance pots on output tubes
- Adjustable bias resistor on output tubes per channel
- Heater hum pots
- Adjustable B+ voltage (tapped resistors in power supply)
- Teflon insulated wire

https://www.diyaudio.com/forums/atta...6-jpg-jpeg-jpg

It's also built with all the RIGHT parts. Here's what's in it:
- Stancor (Chicago Standard) PC-8412 400-0-400V power transformers
- RCA 5V4G/GZ32 rectifier tubes
- Thordarson 20C56 8H 200ma chokes
- Acrosound TO-300 Ultralinear output transformers
- Mullard old-stock EL34 output tubes
- RCA 12AX7A phase inverter tubes
- Amperex mesh-plate EF86 tubes
- Sprague Atom 100uf 100v cathode bias caps
- Pyramid oil-filled coupling caps throughout

https://www.diyaudio.com/forums/atta...8-jpg-jpeg-jpg

https://www.diyaudio.com/forums/atta...9-jpg-jpeg-jpg

https://www.diyaudio.com/forums/atta...1-jpg-jpeg-jpg

As you can see, this one was built to the nines, by a real craftsman. The layout is pretty much flawless from a technical standpoint- from quiet to noisy as you go from one end of the output chassis to the other, and the power supply is the same.

https://www.diyaudio.com/forums/atta...7-jpg-jpeg-jpg

This amp has been checked out, and parts that were out-of-spec were changed, only as needed. This required replacing all the electrolytic caps (they had excessive DCR), and two of the output tubes, but everything else is as-built,. and in-spec.

The amp sounds wonderful (very smooth, detailed sound with great imaging and very powerful, controlled bass that goes deep), and it's virtually noise-free (no hum at all- and you literally have to stand with your ear in the tweeter of most speakers, to hear ANY hiss or other noise at all from this amp- and then only if you're in a completely quiet room with no surrounding noise AT ALL).

This is what I would call an "heirloom quality" build- something that would be worth passing down to future generations. An example of "Can-do" spirit, and an exceptionally performing piece of audio equipment as well.

Selling for $800.00 plus shipping. US shipping only (no international shipping).
Thanks!

Regards,
Gordon.

GordonW 6th July 2018 03:52 PM

Sold.

Regards,
Gordon.


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