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5687 tube-based preamp with Tung-Sol Black plates, Sylvana and Phillips ECG tube pair
5687 tube-based preamp with Tung-Sol Black plates, Sylvana and Phillips ECG tube pair
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Old 19th July 2014, 05:25 PM   #1
networld is offline networld
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Join Date: Nov 2011
Default 5687 tube-based preamp with Tung-Sol Black plates, Sylvana and Phillips ECG tube pair

Up for sale, a 5687-based tube preamplifier, along with three different sets of tubes. The tubes themselves have quite a bit of value for this price. It is a fantastic preamp I have been using with my Firstwatt F2 clone for several years now with a fostex single-driver speaker setup. Here is the original description:

"It's wired entirely P2P except for the filament regulator board. It's actually a two chassis affair:

The power supply chassis consists of a radioshack 25v/0.45 amp transformer for the high voltage supply, followed by a voltage doubler, bridge rectified into 2x 1000uF 200V caps. These are filtered CLC style by a Hammond 156L 5H 75mA DC Choke into another 470uF 300V capacitor. This outputs ~250v. The filaments are regulated by a Tread with ~4700uF capacitence and a LM317 regulator. This provides 24v for the tube filaments (they're wired in series).

The main power is provided by a AC wallwart. The two chassis are interconnected by a custom cable using 4-pin CB connectors, with the wires covered in techflex.

The preamp chassis consists of the 2 sets of tiffany-style input jacks. These are switched by a fairly nice toggle at the front. This feeds 50k fake-blue-velvet potentiometer, which in turn feeds the 5687's (NOS JAN from Thetubestore.com). They're configured as a simple paralelled single-ended triode gain stage. The resistors are vishay dralorics for the low wattage (1/2 watt or less) and 1 watt Carbon Films from mouser for the higher wattage resistors. I used dayton coupling caps for the output, and bypassed the high voltage supply with 4.7uF + 0.47 uF polypropylene and mylar caps, and the low voltage has 220 or 470uF on the filaments.

Each chassis is a 4"x6" Bud aluminum boxes with covers and feet. The amps could easily be finished and painted if you wanted them to look nicer. You'd just need to unscrew the transformer and choke and tube clips, and cover the holes to do it.

If I recall, this can provide ~20V of drive, with virtually no distortion. It was based on an article for an inexpensive tube preamp in Audio Express magazine. I added some of my own touches, including the regulated filament supply.

If you wanted to turn it into a good headphone amp, the easiest way would be to use a +/- 12v power supply to power two Intersil 5002 buffers. Just connect those at the output -- the tubes provide the voltage drive and the buffers handle the current. This would give you a millet-style hybrid, only way better (no big electrolytic coupling caps, real HV tubes on the front-end)."

PM with any questions.
PRICE DROP
$125 shipped and pay-paled within the continental USA
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Last edited by networld; 23rd July 2014 at 06:58 PM.
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Old 30th July 2014, 01:23 PM   #2
networld is offline networld
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Join Date: Nov 2011
bump, still available!
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Old 31st July 2014, 10:34 AM   #3
hatrack71 is offline hatrack71  United States
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Location: Helena, MT
I'm interested. PM sent.
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Old 10th August 2014, 01:23 AM   #4
6L6PPP is offline 6L6PPP  United States
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Location: Mount Vernon, Ohio
Is this preamp sold????
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