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Old 22nd July 2007, 03:17 PM   #1
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Default need help finding a link . . .

I've searched here, and on the net . . . I had found it by accident months ago, but stupidly did not bookmark it.

it was a DIY 45 SET amp, which used PP OPT's from a Fisher or Sherwood receiver (I think). The builder's reasoning was a 45 tube would not come close to saturating the higher Ma-rated PP OPT . . .

I have some 45 tubes, and some cool old military 6L6 OPT's, so I though I'd give it a shot . . .

anyone got a link to the schematic, or webpage ?

thanks for any help !
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Old 22nd July 2007, 06:15 PM   #2
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I think you are referring to an old Glass Audio article called "Single Ended Glory for Under $100"
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Old 23rd July 2007, 04:25 PM   #3
kevinkr is offline kevinkr  United States
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I remember the article too in Glass Audio I think possibly by Eric Barbour?? It was the inspiration for my first foray into SE amplifier design. Mine was also a 45 SE design which used PP output transformers from an old Eico HF-81 integrated amp.

I was trying to discover whether or not there was anything to what I perceived as hype around the SE vs PP argument. I didn't have much money to invest at the time so this was a cheap way to find out for myself - not liking to build someone else's design I came up with my own.. The results were quite good and I still have the amp almost 10yrs later. The unit also has a regulated tube based power supply and operates with fixed bias - unconventional for SE amps at the time. The transformers are good enough that I have never been motivated to replace them.

I wrote an article about the project which is on my site, along with some really bad pictures of the amp.

http://www.kta-hifi.net/projects/amp...ht/45_dht.html

(If you do build something similar get a power transformer with a bias tap - don't use the capacitive type voltage divider I used, it took me a long time to find caps that stood up to that use.)
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Old 24th July 2007, 06:21 PM   #4
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AH HA ! ! !

YOUR site Kevin is the one I had stumbled upon - thanks for the link : )

The Army Signal Corp OPT's I have are 9000 Ohm Primamy . . they have speaker taps for 30, 60, 125, 250, and 600 Ohm. I figure I'll use the 30 Ohm tap with an older pair of 16 Ohm speakers, and go off the 45 tube data for operating points:

Class A Amplifier
Plate Voltage ................................. 275 V
Grid No. 1 Voltage ............................ -56 V
Amplification Factor .......................... 3.5
Plate Resistance (approx) ..................... 1670 Ω
Transconductance .............................. 2100 µMho
Plate Current ................................. 36 mA
Load Resistance ............................... 4600 Ω
Power Output (approx) ......................... 2 W

I have power and filament transformers coming out of my ears, so that wont be an issue . .

looks like it's time to go capacitor shopping
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Old 24th July 2007, 11:32 PM   #5
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by bottom_feeder
AH HA ! ! !

YOUR site Kevin is the one I had stumbled upon - thanks for the link : )

The Army Signal Corp OPT's I have are 9000 Ohm Primamy . . they have speaker taps for 30, 60, 125, 250, and 600 Ohm. I figure I'll use the 30 Ohm tap with an older pair of 16 Ohm speakers, and go off the 45 tube data for operating points:

Class A Amplifier
Plate Voltage ................................. 275 V
Grid No. 1 Voltage ............................ -56 V
Amplification Factor .......................... 3.5
Plate Resistance (approx) ..................... 1670 Ω
Transconductance .............................. 2100 µMho
Plate Current ................................. 36 mA
Load Resistance ............................... 4600 Ω
Power Output (approx) ......................... 2 W

I have power and filament transformers coming out of my ears, so that wont be an issue . .

looks like it's time to go capacitor shopping
Cool, glad I was able to help. I use the 16 ohm taps on the particular transformer I used in order to reflect 3.9K: 8 ohms and since the transformers also have 32 ohm taps I can match all the way from 2 0hms (why lol?) to 16 ohms.. Your load will result in a good balance between power, thd and damping factor - and you should get slightly more than the 1.6W I get out of mine..

Don't hesitate to ask if you have any questions.. This is still one of my all time favorite amplifiers, it still sees regular duty at meets and the occasional party with the old Jensen 3 ways.. (Not quite up to driving the Onkens and their complex x-overs although it is passable I guess.)
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Old 25th July 2007, 01:55 PM   #6
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thanks Kevin : )

I think I settled on a Power transformer - ratings are bigger than the one you ised, but I figure with a little more CLC filtering to knock the secondary voltage down, it'll work nicely.

It's a BIG 40's era PT with the following taps:

850VCT @ 300ma
310VCT @ 50ma
32V @ 10A
6.3V filament tap
5.0V filament tap

I have a few others to choose from, but I think it'll be kinda funny to have a 80 pound amplifier that puts out about 2 watts pr channel. I have a HUGE stash of HV oil caps for the power supply, and a couple big 15 H chokes.

I'm sure I'll be picking your brain on this one



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