hi-fi project?

[rdrgtr]

I hope I am not crossing the line here.  While going through my piles of stuff, I found a couple of mono block hammond amps.  I pulled the OTs from them and plan on making a stereo hi-fi amp.  I guess I can give the guitar amp buiding a rest for a little while.  Anyhow, these trannys will deliver around 40 to 50 watts a piece.  I would like to use el34s or 6550 tubes if possible.  Unfortunately,  they do not have ultra-linear taps on them.  I also dug up a 100 watt PT to fire up the project.  Any schematics or ideas?  I thought I would ask you guys first before I hopped on to one of the those hi-fi forrums.  Besides, you guys are the smartest people I know...

[jjasilli]

Do you know what amps the OT's came from?  The point:  I think for hi-fi you want to closely match the plate-to-plate impedance of the power tubes to the nominal impedance of the OT primary.  That's a big difference from el34 to 6550.  My suggestion is to use the same type of power tube that Hammond used with these OT's. 

What year were these trannies made.  Before 1958 or so, OT's did not cover the full audio spectrum, often being limited to say 100Hz to 10,000Hz.  Still good for some types of music, but not truly hi-fi.  Really good trannies are from the early '60's, and with tight laminations (not the open wound ones). 

Anyway, design backwards.  If the trannies are desirable for hi-fi, then pick matching power tubes.  That will determine the input voltage swing you need from the PI, usually a concertina.  They are great for hi-fi, being simple and very linear.  That could be your whole mono bloc power amp.

[DummyLoad]

probably a PR-40 or the like cabinet - they are full range. have fun.

may i suggest a pair of williamson ckts? see attachment. there are better copies in cyberspace - search "heathkit W-3"

peace.

--DL

[PRR]

> a couple of mono block hammond amps.  I pulled the OTs from them

Why?? The Hammonds are good-sounding amps. The parts were mostly excellent. The heavy work is already done. Dual-mono is more-sexy than stereo on one chassis.

[rdrgtr]

The dual mono would be cool, but those 2 chassis have been gutted over the years.  After further review it looks like the amps had 8 6v6 tubes in it.  There were two amps in each (4 6v6 for each tranny. 16 6v6 tubes for the 2 amps combined!)  The chassis are big and bulky with loads of sockets.  Each had 2 5u4 in them as well.  I am not sure of the date of these amps though...

[rdrgtr]

Here is the schematic.  The OT's I have are the ones for the bass cabinet.

[HotBluePlates]

Do you still have the PT and chokes from the original chassis?

The dedicated OT for the bass has me a little worried for you. I wonder if there is any real issue with the treble response of those, or if they're just bigger than the treble OT's (to go lower), and don't have the feedback winding.

[DummyLoad]

they do have dissimilar part number - as you say HBP, they are likely different parts.

geetar amp! use the treble OT  and build 4 x 6V6 princeton reverb.  wheeee!!!

[HotBluePlates]

geetar amp! use the treble OT  and build 4 x 6V6 princeton reverb.  wheeee!!!

From the sound of it, he only had the bass OT's left. But I might have misunderstood him.

[rdrgtr]

I do have the large chokes and the small treble output transformers.  The small chokes I used in previous builds.  I was drawn to the larger trannys from appearence alone.  I performed a test.  I put an amplified pink noise signal into the primary and monitored the secondary with a RTA and the response was surprisingly flat.  I wonder if the transformer was large to meet the power demands from the bass cabinet.  It looks like they had a primitive eq in the rotary switch (bass correction).