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
That’s too much….how couldn’t I notice it at the time?
So I’ve begun to re-read info in the thread and understand that correct B+ should be around 390V, I’m roughly 30V too high so how do I lower B+?
First have reduced C4 from original 20uf to 10uf, B+ changes from 422V to 413V…..good but still not enough and that why I’m 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?
Don’t know, what do you think? Any help will be greatly appreciated.
Regards
g.
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
That’s too much….how couldn’t I notice it at the time?
So I’ve begun to re-read info in the thread and understand that correct B+ should be around 390V, I’m roughly 30V too high so how do I lower B+?
First have reduced C4 from original 20uf to 10uf, B+ changes from 422V to 413V…..good but still not enough and that why I’m 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?
Don’t know, what do you think? Any help will be greatly appreciated.
Regards
g.
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."
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.
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.
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.
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
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
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.
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.
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.
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.
itsikhefez....zxx222....OldHector....cogitech....
sorry folks I was wrong while zxx222 and itsikhefez were absolutely right : 420V and 70mA are way below max permitted with these tubes (see doc attached)
So that's now my configuration, running happily and sounding very good.
Well anyway I've learnt something and received good counseling, thanks all and sorry for the inconvenience.
As soon as burn-in is finished will report listening impressions but from now I can say these tubes sound detailed and delicate, while bass is present and controlled.
More in two or three weeks.
Thanks again and stay well
g.
sorry folks I was wrong while zxx222 and itsikhefez were absolutely right : 420V and 70mA are way below max permitted with these tubes (see doc attached)
So that's now my configuration, running happily and sounding very good.
Well anyway I've learnt something and received good counseling, thanks all and sorry for the inconvenience.
As soon as burn-in is finished will report listening impressions but from now I can say these tubes sound detailed and delicate, while bass is present and controlled.
More in two or three weeks.
Thanks again and stay well
g.
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