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Old 6th April 2020, 06:39 PM   #1
gmonno is offline gmonno
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Default TSE B+ too high

As you may have red, a couple of weeks ago had a problem with (probably) a loose screw that reverted in problems with Q2 and U2. Talking about my loved TSE 300B.
Ended with a bad 300B, now I have new Emission Labs 300B.
Doing all routine checking (175V on 5842 plate, around 60mv on 300B plate..) I discovered a little, a small, an insignificant detail that surely passed unnoticed when TSE was built, 5 years ago : a B+ of 422V
Thatís too muchÖ.how couldnít I notice it at the time?

So Iíve begun to re-read info in the thread and understand that correct B+ should be around 390V, Iím roughly 30V too high  so how do I lower B+?

First have reduced C4 from original 20uf to 10uf, B+ changes from 422V to 413VÖ..good but still not enough and that why Iím asking for your help.

Any suggestion how could I reduce B+?

For example, would it help :
- a couple of CL 90 thermistor on both legs of transformer?
- add another R-C to the C-L-C rectifier after C5?
- add a resistor after or before the choke?

Donít know, what do you think? Any help will be greatly appreciated.

Regards

g.
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Old 6th April 2020, 06:47 PM   #2
cogitech is offline cogitech  Canada
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TSE B+ too high
One solution would be to drop in a 5U4 or 5Y3 rectifier in place of the 5AR4. However, you'll want to make sure your power transformer can handle any extra current a new rectifier might draw and also adding a CL-90 to slow things down would be essential in this scenario. You want the power tubes hot before they get too much juice from the rectifier.

As per George's common on the TSE page "The amp will work with other rectifier tubes (5U4, 5Y3 etc) but I like the 5AR4 because it is very slow to warm up, which gives the other tubes plenty of time to get hot before the B+ comes up."
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Old 6th April 2020, 07:17 PM   #3
gmonno is offline gmonno
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Quote:
Originally Posted by cogitech View Post
One solution would be to drop in a 5U4 or 5Y3 rectifier in place of the 5AR4. However, you'll want to make sure your power transformer can handle any extra current a new rectifier might draw and also adding a CL-90 to slow things down would be essential in this scenario. You want the power tubes hot before they get too much juice from the rectifier.

As per George's common on the TSE page "The amp will work with other rectifier tubes (5U4, 5Y3 etc) but I like the 5AR4 because it is very slow to warm up, which gives the other tubes plenty of time to get hot before the B+ comes up."
Thanks, that's why I'd like to leave 5AR4 in place and use any other solution.
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Old 7th April 2020, 05:50 AM   #4
OldHector is offline OldHector  Sweden
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Plenty of food for thought here ...
how-to-properly-reduce-b
I have a NTC varistor before the primary (cl90) and after the secondary (cl140). Do you have a choke and motor run supplementary capacitor? With a 5AR4 rectifier, my SSE has a nice soft start.
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Old 7th April 2020, 06:42 AM   #5
itsikhefez is offline itsikhefez  United States
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TSE B+ too high
I think 2 of your last options should work well....
I too had high B+ and adding a chassis mount resistor in series with the inductor helped reduce it.
I ended up using tomchr's HV Maida regulator in that amp, with it I was able to dial-in B+ exactly.
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Old 7th April 2020, 06:47 AM   #6
gmonno is offline gmonno
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Maybe I could change from a C-L-C (capacitor input) to a choke input?

This may help as I've read that Vdc would multiply to 0,9 (choke) instead to a 1,3 (cap)
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Old 7th April 2020, 06:49 AM   #7
itsikhefez is offline itsikhefez  United States
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TSE B+ too high
That is also possible, although from what I read (not from my experience) that requires a much beefier choke than ones typically used...
For example, ISO sell different chokes whether they are cap input or choke input.

If you have one, great. Otherwise, I would go with CLRC or CLCRC.
One bonus with adding a resistor is that it should knock down PS ripple a bit more
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Old 7th April 2020, 08:09 AM   #8
gmonno is offline gmonno
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Thanks all !!

Will use your suggestions and think what to do --> will let you know.
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Old 7th April 2020, 08:16 AM   #9
itsikhefez is offline itsikhefez  United States
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TSE B+ too high
Good luck!
By the way, on the EML website they provide operating points for the 300B for 400V and 450V, so maybe 420V will be OK ?
300B tube data sheet. Emission Labs.
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Old 7th April 2020, 09:52 AM   #10
zxx222 is offline zxx222  Europe
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You have some voltage drop on primary of OPT (5-10V, depending on primary resistance).

If your 300b's are biased at 60mA, dissipation with 422V B+ is 25W and that is way below 36W recommended max for EML tubes, no reason to worry. You could bias them hotter - that will drop some voltage as well.
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