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Hi fellow Tramp enthusiasts,

As I mentioned in another thread, the mains voltage in my house is a bit high (Just now I measured it at 123.8V) resulting in slightly higher voltages in the amp. I've noticed that the voltage on the first filter cap (C13) exceeds its 450V rating depending on where the VRM is set. Here are a few measurements of this voltage that I took at different positions on the VRM dial:

VRM at Idle: 460V
VRM at 5: 456V
VRM at 7: 452V
VRM at 9: 440V
VRM at Max: 431V

This doesn't seem too safe to me, but what do some of you more experienced builders think? Perhaps I'd sleep a bit easier at night if I increased that cap to 500V.

Thanks in advance for any replies!

I think the voltage needs to get dumped. In the resource section there is a post on building a voltage dumper. Basically a Zener diode on the Center tap of the PT to ground.
For whatever reason, the B+ is high and exceeding the voltage of the filter caps is not ideal. It's a simple and cost effective solution. You want the B+ to be about 400 or so. So take of 20 or 30 volts.

Also, the VRM at max should be higher than at min, so what going on there?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

The tubes are not installed are they?

Install the tubes and the VRM readings will be more normal and the B+ will go down to ~400V.

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http://pdfelectronics.com

Thanks for the replies.



It's actually not the B+ voltage I'm referring to (correct me if I'm wrong)...the other filter cap connected directly to the rectifier diodes. I've attached a picture to illustrate the location.

My B+ seems to be OK. Here are some readings I took the other night of BOTH the high voltage I'm concerned about and B+. Note that 450 volts wasn't exceeded at this time...I'm guessing because my mains voltage was a bit lower. However, it still sits pretty close to the rated value .

Mains: 120.8

VRM Idle: C13 Voltage = 441, B+ = 42
VRM 5: C13 Voltage = 440, B+ = 72
VRM 7: C13 Voltage = 437, B+ = 107
VRM 9: C13 Voltage = 426, B+ = 260
VRM Max: C13 Voltage = 416, B+ = 407

I'll have a look at the voltage dumper later on tonight.



Yes the tubes are installed.

B+ voltage dumper. viewtopic.php?f=12&t=3218

What are your voltages measured where on the layout says 400 I.e. B+. ?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

In my previous post I included my B+ (measured at the 400 on the layout). They look to be alright.



Thanks

Ahh, so it looks like the B+ voltage dumper method should do the trick for me. I'll order a few different values of 5W zener diodes in the 20-30V range to see what works best. Is there any need to heatsink the diode?

No heat sinking required.A 5w is a good Idea.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

The diodes came in today and I ended up using a 28V, 5 watter. It did the trick nicely . Thanks guys.

Good stuff . You might make it switchable so you can throw in a 6l6 in there with the higher voltage. That tube will pull the voltage down anyway.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps