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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Copland CTA-501 NOS Tubes posted by Harbord on June 22, 2004 at 03:06:24:
... and in the CTA-401 the ECC83 is used - one triode system per channel - as voltage amplifier. In each channel it is followed by one ECC82 as long tailed pair phase splitter/driver and two EL34 as push-pull power amplifier stages.The CTA-401 has as well an RIAA-section which uses one ECC83 per channel.
Concerning the power amp section, the following bits hat a big influence on the sound quality:
(1) Replacement of the run-off-the-mill Chinese E82CC by Silvania 6189W selected for good symmetry (three point match) - or alternatively Telefunken <> ECC802S selected for good pair symmetry. Siemens triple Mica E82CC did not convince me in this position - neither Telefunken <> ECC82/12AU7A
(2) Replacement of the Chinese 12AX7WA/E83CC by a Siemens E83CC (early 1969ies version - German Rundfunk stock selected for low microphonics). Alternatively - this gives a warmer, more laid-back, but as well less resolved soundstage - a Tesla early 1980ies frame grid E83CC (the Telefunken ECC803S copy) - again selected for good symmetry. I tried the box anode Mullard CV4004/M8137 in that position - not to my liking. Neither did the Telefunken <> 'long plate' or 'ribbed plate' ECC83 work. The GE 7025 was way too bright as well.
(3) Output valves - the unit came with well-matched but worn-out Svetlana =(C)= EL34s. Replacement with well-matched (three-point match in slope and idle current) Svetlana EL34s was a big step forward. Did not care for EH EL34 with similar match - way too forward and bright for my ear. Philips/Mullard EL34s were very nice, too, having similar character to the Svetlanas - slightly better, but not worth the huge price difference. RFT Muehlhausen EL34s (with Siemens label) were quite disappointing in comparison - sounded like somewhat better EHs... Did not try China-EL34, EI-EL34s or real Telefunken Ulm.
(4) Important is the right bias adjustment - bias current works for me best at about 45..50 mA (450mV..500mV between cathode and ground) - more I did not care for, getting too mushy, and less leads to a slightly cold sound at medium to high volume. Good symmetry is paramount - it improves the quality of sound significantly.
Best regards,
---mb---
======
PS:
(1) I am using the Copland CTA-401 (though higly modified) with Sonus Faber Guarneri Hommage, and a number of analog and digital sources - Revox B760 tuner, Revox A77 and Nagra open-reel tape recorders, T&A 1220R CD-player (filter 4 - using Bezier polynoms), TEAC CD-RW and Alesis Masterlink with SEK'D ADDA2496, Thorens TD147/TP16 record player with EMT MC and step-up transformer- plus an active subwoofer (KEF) (filters by Eckmiller).
(2) For the RIAA stage, the Mullard M8137/CV4004 fits best for my set-up and taste. E83CC from Siemens work well, too.
(3) Siemens never made EL34s in any sizeable quantity. They bought OEM EL34 valves from Philips/Mullard, Telefunken (rare), RFT Muehlhausen factory and EI Yugoslavia (normal and dimple top). Which ones do you have?!
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Follow Ups
- The Copland CTA-401 is a similar design... - mb-de 07:07:27 06/22/04 (1)
- Re: The Copland CTA-401 is a similar design... - Harbord 02:59:29 06/23/04 (0)
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