Which EL34/KT88 PP projects should I consider? - diyAudio
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Old 11th January 2017, 03:37 PM   #1
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Location: Victoria, BC
Default Which EL34/KT88 PP projects should I consider?

I want to build a PP amp with either KT88 or EL34 (or possibly 6L6GC?) tubes.

The main 'candidates' on my list right now are:
Pointz (AudioTropic) Musical Machine with 6GK5 and EL34 tubes.
http://usr.audioasylum.com/images/2/...o_Shematic.jpg
EDIT: this is the wrong schematic, sorry.

Allen Wright KT88 PP2C but building it without the 'SuperReg' - using the same type of power supply as in the PP1C:
PP2C
http://basaudio.net/gm70/index.php?a...9.0;attach=205
PP1C Power Supply
http://www.vacuumstate.com/images_up...pp_1c_ps_s.gif
or Allen Wright EL34 PP1C
http://www.vacuumstate.com/images_up...ss/pp_1c_s.gif
I've read a couple of cryptic comments that the Musical Machine has 'design problems', so I'm wondering about that.

I'm not interested in very complex power supplies that need PCBs and a lot of SS regulation (like the SuperReg), though I have no problems with wiring up something on terminal strips or perforated board- like the CCS in those amps.
I won't be buying 'audiophile grade' capacitors and resistors.
Output transformers will be coming from my parts shelf (Fisher and similar) or ordered from Edcor.

Speakers will be Troels Gravesen DTQWT or AudioNirvana 10s - both in the 95dB sensitivity range.

I already have an EL34 SE amp, and some other SE projects on my list, so concentrating on PP designs for now.

What other designs do you think I should add to my list for consideration?

Thanks!

Last edited by VictoriaGuy; 11th January 2017 at 10:15 PM.
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Old 11th January 2017, 04:12 PM   #2
20to20 is offline 20to20  United States
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Why not do a little research on some historically significant circuits and try one of those? Early '50's, mid '50's based on Williamson. Plenty of interesting and fine amps in Acrosound tranny catalogs and old Radio Electronics magazines
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Old 11th January 2017, 04:15 PM   #3
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8 WPC is plenty for 95 dB. sensitive speakers. KT88s are overkill. 7591s are as easy to drive as "12" W. tubes. Triode wired 7591s should prove ample, for your purposes.

Poinz's "Musical Machine" would do nicely. A "taller" B+ PSU and different O/P "iron" are the changes need to switch from the "12" W. 6V6 to the "19" W. 7591.
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Old 11th January 2017, 04:15 PM   #4
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Mullard 5-20 for example.
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Old 11th January 2017, 04:36 PM   #5
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Tubelab FTW! Tubelab SSE | Tubelab
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Old 11th January 2017, 05:22 PM   #6
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Quote:
Originally Posted by danconway327 View Post
That one is SE not PP. They do have a SPP but I don't see it being built as much on here so there isn't as much experience to feed off of.
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Old 11th January 2017, 05:25 PM   #7
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Thanks for all the quick replies. Love this place!

I found the comment about "problems" with the Musical Machine - it was SY who said:
Quote:
The Audio Tropic design is not without problems. It's basically a Mullard 5-20 with an SRPP substituted for the input tube and the grid stoppers removed. There are a lot of ways of improving it, especially with regard to distortion and source impedance. The SRPP has its niche (high voltage swings into reactive loads), but there seems to be a fascination with it that transcends the actual virtues.
Eli-
I was thinking that I was looking at too high power (KT88) for my speakers but I keep running across comments that the 'extra' is needed for bass, transients, etc.. For example, Troels Gravesen says:
Quote:
My default recommendation for an amp for the TQWT/DTQWT is a PP valve design like the Cayin A50T, A55T, A88T, etc. These amps usually delivering 20-25 wpc in triode mode and 35-45 watts in pentode mode.
There are numerous variants of these KT88/EL34 PP designs, like the Prima Luna and World Audio designs. Use google to find more - and not least countless diy designs on KT88/EL34/6650
I don't want to end up with an amp where I adjust the volume only between zero and 2 (on a 0-10 scale) . I have a SS amp for that!

I thought Williamson designs needed good/very large/specifically wound output transformers?
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Old 11th January 2017, 05:50 PM   #8
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Quote:
Originally Posted by ta240 View Post
That one is SE not PP. They do have a SPP but I don't see it being built as much on here so there isn't as much experience to feed off of.
From what I have read here and elsewhere, SE is better for High efficiency speakers, more so than PP, YMMV.
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Old 11th January 2017, 05:55 PM   #9
20to20 is offline 20to20  United States
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Quote:
Originally Posted by VictoriaGuy View Post
I thought Williamson designs needed good/very large/specifically wound output transformers?
Is that what Williamson used in 1949? Dynaco was built on an improved transformer for Williamson amps. You don't have to get any more esoteric than that type of modern quality. They also explained how to improve the stability and reduce the stages. Lots of good 2-channel mid to late '50's circuits used of the day trannies for Williamson type circuits. But the real improvements came from better driver stage design for less phase shifting allowing more GNF.
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Old 11th January 2017, 06:06 PM   #10
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Quote:
Originally Posted by Eli Duttman View Post
Poinz's "Musical Machine" would do nicely. A "taller" B+ PSU and different O/P "iron" are the changes need to switch from the "12" W. 6V6 to the "19" W. 7591.
So for 7591s, a plate voltage in the 400-450 range and a 6k6 ohm OT?
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