Two Presto 40-B Preamps

[EpicenterBryan]

Hi guys,
I thought I would offer these two Presto 40-B pre-amps here before listing on E-bay.
These were designed to hook directly to the Presto 88A cutting amps, using their B+ and 6.3 volt filament output connections.
If you wanted to run these on their own, you need an external power supply. I measured two 88 amps and the B+ is in the 260v to 280v range. There are supplies on Ebay that can provide both the B+ and 6.3 filament for pretty cheap.
These amps use one 6J7 and one 6SJ7 tubes. Both have Kenyon P400 output transformers. One unit has a UTC LS-10X input transformer, and the other one has a Kenyon P204 input transformer. They are currently wired for 50 ohms in, and 50 ohms out.

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If you look at the front panels, you see cannon connectors - easy to swap out if desired. You also see an RCA cable looping into an RCA jack. That was a mod installed in 1966 to provide a patch point to access the amp output prior to the transformer. Why they didn't just use a normalized jack, I just don't know. In the center of the panels is a hole cover. I think originally there was a switch there to select several output transformer taps. That might make a nice place for adding a gain control.

I have not run these. I think due to age they should just be recapped right off the bat.
Attached is a schematic and data for the Kenyon transformers. I don't have the info for the UTC transformer.

I'm thinking $250 each is reasonable (plus shipping). The same UTC transformer recently sold for more than that alone.

Any interest?

Bryan

[EpicenterBryan]

They are currently wired for 50 ohms in, and 50 ohms out.

Oops, a typo there....
They are currently wired for 50 ohms input, and 500 ohms output.
Looking at the transformer details shows you can change those combinations if needed...

Bryan

[EpicenterBryan]

Sold. Thanks guys.

Bryan