PRESTO RECORDING CORP *Mic Pre*

[EvLoutonian]

Y'ello again folks..

I've got a couple of PRESTO RECORDING co TYPE 40-A (presumably mic) pre-amps.

They are pretty basic, with 50/200/500 ohm input transformer (with single switch on front panel), plus output tranny, and that's about it.
Two tubes: a single 6J7 and a 6SJ7.

Of the two units I have, only one transformer remains (bugger!)
- a single KENYON P400 (output transformer).

So, I'm on the lookout for another (1x) of the KENYON transformers (type "P400") and two of the input transformers, which are:
(2x) UTC LS-10 (or equivalent)

UTC LS-10 specs:
primary inputs: (presumably) 50 / 200 / 500 ohms.
secondary: 60k ohms

I'll include the circuit for anyone interested..
Rob from PRO HARMONICS reckons it's worth tweaking up, but obviously not gonna get too far with 3/4 of the transformers missing!
(:

Any tips or info appreciated.
Cheers,
Evan

[EvLoutonian]

Here's the schematic.
(with image of the unit included)

[rick]

you really hit on the old heavy junk ship didnt you
i would think they are probably more likely cutting preamps
but hell gain is gain

[EvLoutonian]

you really hit on the old heavy junk ship didnt you
i would think they are probably more likely cutting preamps
but hell gain is gain

Mmm, could definitely be the case with these.. But I'm not sure!
Either way, they're sweet little things, that deserve another go at life!
(:

[EvLoutonian]

Just looking back at these now, after a bit of a gap of various this and that's..

A question:
If this was indeed original designed and intended as a record cutting pre-amp, then is the Kenyon (P400) output transformer not necessarily going to be appropriate for (600 ohm line level) output to a desk or multi-tracker?

I'm trying to figure out if it's worth trying to track down a matching Kenyon transformer for the unit which is missing in the second box, or better to just scrap this and get a couple of matching units from elsewhere..

Any ideas, shoot!

[EvLoutonian]

ALSO - I just found this great old source on these (and other Presto gear)!

http://www.preservationsound.com/?p=3162

QUOTE: ..."the Presto 40-A microphone pre-amplifier, the one piece of equipment in this lengthy catalog that could still be of potential use to modern recordists"...

This is encouraging!

Lots of great images of circa 1940 record cutting biz and gear.

[EvLoutonian]

An update for anyone who might be interested..

I found a Trimax output transformer that seems to be a good enough match for the Kenyon output tranny which was missing in the second of the two amps. Primary 20k, secondary 600 ohms.

And I purchased two UTC input transformers, albeit much (much) smaller than the original LS-10's.
The replacements are P-2, with an octal base plug (with same spec as the O-2 from their "ouncer" series).

I've also replaced the plugs, or made adaptors on the ends of the appropriate cables, for XLR input / output.
And plans are afoot for the appropriate power supply connection, to hook up with an old supply I have that should suit the HT and filament requirements.

Here's an image of where I'm at now:
https://fbcdn-sphotos-a.akamaihd.net/hp ... 0273_o.jpg