Sowter Output Iron

[Blair]

I may be purchasing a pair of Sowter outputs for a PPP project.

200 Watts
Ra-a = 1.5k ohms
120mA dc
Secondary for 1, 4, 8/9 or 15/16 ohms

I think 6-8 EL-34s would work well, or 6-8 6L6 tubes.

The output iron is UL tapped.

The thing that gets me when I see specs like these is the 120mA DC.

What is that rating for? 8 EL34 tubes biased at 40mA is 320mA. Granted the DC current rating is per side, so 240mA total, the bias current alone for 8 tubes is higher than the output transformers rating.

Am I missing something?

Also, has anyone ever used Sowter? Are they any good?

Thanks!

Blair

[kheper]

I may be purchasing a pair of Sowter outputs for a PPP project.

200 Watts
Ra-a = 1.5k ohms
120mA dc
Secondary for 1, 4, 8/9 or 15/16 ohms

Blair

Sowter makes high-end iron. I do not see the model number or specs, corresponding to your transformer on their PP output page. Do you have a model number? Their 200W rated output iron has maximums of 275 and 250madc. Make sure you are buying directly from them, not from a con-artist. 120madc will not get you 200W PPP audio output.

http://www.sowter.co.uk/push-pull-outpu ... ormers.php

[Blair]

https://www.dropbox.com/s/d38bysx5xfnoju1/7297.pdf

Just trying this. I emailed Sowter and they sent me this. They are also from a trusted source.

It just seems like the DC current is a bit low for 200W.

Thanks,

Blair

[kheper]

I searched sowter's site for model "7297". No dice. There was nothing relevant in a google search either. 120ma might be ok for 20 watts with 6l6s or similar, but 200W? Maybe someone unintentionally added an extra zero.

[battradio]

I have seen them and they are very large and heavy (more than twice the size of MKIII ). They are at least 20 years old and came from a collection that had a lot of high end amps , I ended up with the power transformers and chokes that where going to be used with them .
If anything they are 200 watt and miss marked on current , with that much core they sure the hell won't saturate at 120 ma .

[kheper]

Those things are huge. They'll do 200W in PPP. Sowter does not currently produce them. I wonder what they would charge to make them now? Think they could handle 320ma per transformer?

[battradio]

I realy think 120 MA is a miss print

[tomlang]

Ra-a = 1.5k ohms! Try a pair of 13GB5's. I just posted a low power version viewtopic.php?f=3&t=5846 using 1200 ohm OPT's.

"Tubelab" George is getting 67 watts out of a pair them with 1250 ohms, twice that if connected as 2500 ohms...

http://www.diyaudio.com/forums/tubes-va ... ost3249737

[Blair]

Hey now! Off the iron! LOL!

I have a few pairs of 100W outputs for sale from a MO-200 if anyone is interested.

Blair

[soundbrigade]

a) I have a pair of Russian monoblocked PPP:s in the closet. Rated 50 ... 60W with three pairs of 6L6 each channel. Trannies are special made Russian. One of the blocks has an intermittents error which is bad as they can drive almost anything with their ridicolusly low Zout. They still deliver 20W at 200mOhm load. Going for a Circlotron is definitely a good idea!

b) This (http://www.experience-electronics.de/) company also sells transformers for PPP-amps.

[Blair]

I had the guy I'm buying these from measure the DCR of the primary, and it is 11.5 ohms. So, I think it is safe to say, as Mark has suggested in private email, that the mA rating must be DC offset.

I finally coughed up enough to buy them, so they will be on their way this week.

Anyway, I plan to use these with a choke input from a pair of Hammon 193Q choke and a pair of big Western Electric KS-8878 power transformers.

The power transformer specs are not obtainable by any means I know, but Battradio(who I got it from) thinks they are good for over 500mA with a choke input. I sourced a second one out of luck, so I need to purchase it.

I should net, with a choke input, around 520-540VDC B+. So, with a 1.5K primary, what tube will work best? I have had a few folks suggest 8 KT88s per channel, but looking at the data, that would be with fixed bias.

Would 6 KT88s work into 1.5K in UL at 540V? Lastly, is 500mA enough guts to drive the KT88s to full power?

Thanks!

Blair

[battradio]

picture of the power transformer .

[Blair]

:) and if that's not a good scale reference:

[kheper]

Anyway, I plan to use these with a choke input from a pair of Hammon 193Q choke and a pair of big Western Electric KS-8878 power transformers.

The power transformer specs are not obtainable by any means I know, but Battradio(who I got it from) thinks they are good for over 500mA with a choke input. I sourced a second one out of luck, so I need to purchase it.

I should net, with a choke input, around 520-540VDC B+. So, with a 1.5K primary, what tube will work best? I have had a few folks suggest 8 KT88s per channel, but looking at the data, that would be with fixed bias.

Would 6 KT88s work into 1.5K in UL at 540V? Lastly, is 500mA enough guts to drive the KT88s to full power?

Thanks!

Blair

Bonavolta has a somewhat similar amp: 1ohm Raa primary.

http://www.bonavolta.ch/hobby/en/audio/kt88_7.htm

http://tubes.nekhbet.com/power.html#fulwc

If the WE has a 500ma AC secondary - with a FW choke input, you should yield about ~760ma DC capacity.

[Blair]

Holy!!! 5 pairs! That's a bunch of tubes.

I do like the schematic though. You think three pairs would go well with 1.5K a-a?

The MKIII used a 4.2K transformer for 60W, so maybe a little less power per pair, but maybe 150W?

I once used a Hammond 1650W (1.9K) with a Poseidon front end and it hit around 153W before clipping onset at 1K. Back then I did not have a real tone generator, so I had a chip thing I built that put out a 1K sine wave only.

You think it would work out OK with the Sowters? I like that front end on that schematic, but I'd probably swap it out for 6CG7s.

Thanks!

Blair