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Old 13th February 2018, 03:00 AM   #11
Eli Duttman is offline Eli Duttman  United States
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While shipping magnetics long distances can be "dicey" business, it's hard to better AnTek in the price dept.

AnTek's AS-2T300 has more than enough stones for this job. Connect the HT windings in parallel and bridge rectify with 4X pieces of this part or a flat pack equivalent. Schottky's are dead quiet and the need to replace is most unlikely.

Use resistors to create a pseudo CT on 1 of the 6.3 VAC windings.

BTW, Chinese 5U4 "equivalents" are guano. A crappy rectifier could have wrecked the power trafo.
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Old 13th February 2018, 03:11 AM   #12
kevinkr is offline kevinkr  United States
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Since the Hammond is locally available I would just get one and get it over with. It should fit with a minimum of modification.

The Antec Eli suggests is a good option, but I imagine the shipping to the UK will reduce the difference in cost considerably. If you do go that route make sure you have sufficient room and purchase a cover.

I expect Sowter is more expensive than the Hammond, but I would check with them too.

The economics are skewed, if it sounded decent to you you can regard it as having more utility value to you than what you paid for it.

OR

Just put the money towards a new and better amp. Maybe build one of Tubelab's amp projects.
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Old 13th February 2018, 03:27 AM   #13
kodabmx is offline kodabmx  Canada
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Originally Posted by Eli Duttman View Post
BTW, Chinese 5U4 "equivalents" are guano. A crappy rectifier could have wrecked the power trafo.

Have you tried the Soviet 5U4C?
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Old 13th February 2018, 06:02 AM   #14
Eli Duttman is offline Eli Duttman  United States
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Originally Posted by kodabmx View Post
Have you tried the Soviet 5U4C?
AFAIK, the only decent made in Russia 5U4 variant is New Sensor's 5U4GB. The number of reported problems with Russian and Chinese made ST bottle 5U4 "equivalents" is large. You may have come up with a "sleeper".
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Old 13th February 2018, 09:41 AM   #15
6A3sUMMER is offline 6A3sUMMER  United States
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The 5U4 rating is 75 Ohms effective resistance in each plate (Turns Ratio x Primary DCR) + (DCR secondary to CT).

i.e., 300Vct to 220V, turns ratio = 300/220 = 1.36. If the primary DCR is 30 Ohms, that part of the effective resistance to the plate is 30 x 1.36 = 40.8 Ohms. If the CT to one side of the secondary is 35 Ohms, the resistance to the plate is 40.8 + 35 = 75.8 Ohms.

If you have more than 40uF in the first capacitor after the 5U4, you need more than 75 Ohms effective in each plate. Otherwise, the rectifier may go bad or even short.

Last edited by 6A3sUMMER; 13th February 2018 at 09:43 AM.
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Old 13th February 2018, 10:20 AM   #16
onokun is offline onokun  Russian Federation
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Originally Posted by Eli Duttman View Post
Use resistors to create a pseudo CT on 1 of the 6.3 VAC windings.
Hi, is there a particular reason to make ct only on 1 of the heater windings, not on all of them?

Asking because I'm building an amp with 2 heater windings right now.
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Old 13th February 2018, 01:13 PM   #17
Eli Duttman is offline Eli Duttman  United States
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Originally Posted by 6A3sUMMER View Post
The 5U4 rating is 75 Ohms effective resistance in each plate (Turns Ratio x Primary DCR) + (DCR secondary to CT).

i.e., 300Vct to 220V, turns ratio = 300/220 = 1.36. If the primary DCR is 30 Ohms, that part of the effective resistance to the plate is 30 x 1.36 = 40.8 Ohms. If the CT to one side of the secondary is 35 Ohms, the resistance to the plate is 40.8 + 35 = 75.8 Ohms.

If you have more than 40uF in the first capacitor after the 5U4, you need more than 75 Ohms effective in each plate. Otherwise, the rectifier may go bad or even short.
Quite true. My loathing of Russian and Chinese ST bottle 5U4 "equivalents" stems from the many times I've helped people with power on arcing. The 1st filter cap. was within documented limits and switching to a U.S. made 5U4GB ended the "fireworks".
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Old 13th February 2018, 01:16 PM   #18
Eli Duttman is offline Eli Duttman  United States
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Originally Posted by onokun View Post
Hi, is there a particular reason to make ct only on 1 of the heater windings, not on all of them?

Asking because I'm building an amp with 2 heater windings right now.
I made the suggestion to bring things in line with the failed OEM part. Look at the very 1st post in this thread.
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Old 13th February 2018, 02:35 PM   #19
00940 is offline 00940  Belgium
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I priced a custom transformer with your specs (toroidal though) from audiophonics. It comes to 95€ (200VA, 7 windings total, two windings above 100V and electrostatic shield). Not cheap but cheaper than Hammond.

If you used a separate transformer for the 5V (15VA transformers can be found very cheap), you could step down to a 150VA/6 windings transformer which only cost 72€ (66€ without the shield).

I've had decent experience with these. They're a bit slow to ship if you miss the time when they order a batch.

edit: I assumed that the specs you gave were for AC current rating. Some manufacturers, such as Hammond, rate the current of the HV winding for DC.
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Last edited by 00940; 13th February 2018 at 02:47 PM.
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Old 13th February 2018, 05:22 PM   #20
kodabmx is offline kodabmx  Canada
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Originally Posted by Eli Duttman View Post
AFAIK, the only decent made in Russia 5U4 variant is New Sensor's 5U4GB. The number of reported problems with Russian and Chinese made ST bottle 5U4 "equivalents" is large. You may have come up with a "sleeper".
I'm talking about NOS Soviet tubes such as Winged C or Reflektor, not new production.
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