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tigro 7th December 2008 03:58 PM

Upgrading output transformers
I have Antique Sound Lab AQ1008DT monoblocks and thought about upgrading the original output transformers to Tamura
F2011. Did anybody perform a similar upgrade ? I would like
DIY-ers oppinion on the matter.



Jeb-D. 8th December 2008 07:29 PM

Unless it's an exact fit, I wouldn't do it. You wouldn't want to turn your production quality chassis into a hack job.

kevinkr 8th December 2008 08:23 PM

I and others have done similar things on other amplifiers, and at worst to get something that looks nice you just order a nice piece (or 2) of copper or stainless steel plate in the appropriate dimensions online, measure and drill for the new transformers and for some of the mounting locations of the old transformers - if done with care you both stiffen the flimsy AQ chassis and end up with something that looks nice as well.

ASL HK makes very reasonable quality OPTs, but the Tamuras are still likely to be a rather significant improvement if you purchase one of their higher end products.

tigro 9th December 2008 08:55 PM

Dear Jeb

Thank you so much for your answer

tigro 9th December 2008 08:55 PM

Dear Kevin
Thank you for your answer.I'll consider your advice. The Tamura
F-2011 has a primary impedance of 3,4K which is a bit high for
4 KT88-s in parallel push pull.
There might be some Sowter transformers more suitable for this
job. I await Mr. Sowter's answer.



richwalters 10th December 2008 05:51 PM


Originally posted by tigro
The Tamura
F-2011 has a primary impedance of 3,4K which is a bit high for
4 KT88-s in parallel push pull.

This is serious power game. I presume you are upwards 520V B+ region. You won't get optimum throughput power with this Prim Z. You should be aiming around 2K A-A and you will have to take care of ringing with A and g2 snubbers. The best tranny I've used is the Sowter 8659 43% UL with 4 sep o/p windings for optimum quality and b/w.. Study the Sowter website p-p secondary configuration.
Beware they aren't cheap !


tigro 17th December 2008 09:05 PM

Dear rich

Thank you very much for your answer. I already found the Sowter
site and I am in the middle of email exchange with Mr. Sowter Brian. I think I already found something suitable and it also fits the chassis mechanically.



richwalters 17th December 2008 09:40 PM

2 Attachment(s)
The 8659 or variants are large transformers (?10Kg )and particulary smooth response using fixed bias around 60mA per tube. At 2/3 power I got a 10Khz square wave looking in pic. It all depends on the performance of the driver stage. When you get the power stage performing the square wave shown in pic, then you can't ask for more. The distortion is also very low.


Bandersnatch 17th December 2008 11:30 PM

hey Rich,
That is a nice looking response. What sort of amp is in front of it?

richwalters 18th December 2008 03:34 PM

2 Attachment(s)

Originally posted by Bandersnatch
What sort of amp is in front of it?

Both power amps in pic are my strong man studio "Samson & Goliath" class both capable of cruising 200W per channel with KT88's, one has a Sowter 8659 14 sect and other Majestic Partridge spec'd 18 sect, both British wound o/p trannies performing -3dB down around 50KHz. On listening both are close, -, --> I favour the Majestic on iron/winding technicals; requires less A-G2 snubbing but is 10% larger, more consistent construction and goes down to 15Hz and this one has reduced B+ running Tung-Sol 6550's (Rt side).
These heavy amps (each 55kg) are for those who like their music blinding loud or play clean MI (as I do): they use a variable B+ with a PFC converter for economic running. The 12BY7A driver stages & front end Concertina ECF80 are identical.
Those wanting a real UL p-p design challenge in the high end game have got one..every aspect must be math'ed out, including loop gains. Both amps can accept 35dB global nfb before instability sets in. This is a tough challenge as the winding parasitics are much higher than smaller designs, require careful snubbing as the energy is far higher and these amp designs cannot be slapped together as with lower powers. A simple mistake can be expensive in both tubes and patience.
Take note!


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