VTL 75/75 tube amplifier recap (power supply)

[aquila2010]

I use a pic micro to control two 5V 5 Amp relays in series. The first relay turns the power to the B+ transformer on or off the second relay bypasses the CL-80 NTC after one second.

Here is the schematic for what I am using in my GM-70 amp.

MelB, Thank you for the schematic

 

[aquila2010]

It's cheaper to just use one of these: NE555 DC 12V Delay Relay shield Timer Switch Adjustable Module 0 To 10 Second | eBay

Kodabmx thank you for the advice. Did you try it? Is it reliable?

 

[aquila2010]

Hi

in attach the schematic, very simple.
The board has othe sections as negative rail and a HV dide for bridge

Walter

Walter thank you for the schematic.

Please, could you also answer the other questions that I asked you for in my previous post?
Thank you

Thank you Walter,

I'm looking forward to your schematic!
I'd like to use a delay circuit to bypass the NTC by a relay a few seconds after switching the amp on.

If I limit inrush current by using a NTC, what would be a reasonable value of energy storage for the VTL amp? I remind you that It has a pair of KT90 and about 80 watts continous per channel.

At the moment the amp has filter caps connected in series. The B+ is about 555V.
Moreover I'd like to know if I could safely use 600 V caps (NOT in series) like these Nichicons: https://www.digikey.com/product-detail/en/nichicon/LGN2X221MELC50/493-14693-ND/6049397 .
I could put them in parallel to reach the desired value avoiding series cap connection and the consequent increase in series resistance. Unfortunatey, I couldn't find 105°C caps withstanding more than 600V. Using 600V caps my concern is both the voltage peak at switching on, (that is before current starts flowing through the tubes) and the consequence of an increase in mains AC voltage. The latter would reflect on the tranformer secondaries and a 10% increase in the primary would cause 610 V in B+.

On the other hand, I've examined some Audio Research power amps and they use normal 105°C, 450 V Nichicon caps with a B+ of 420 V. A 10% increase in AC voltage mains would cause more than 460 V in B+!

Please let me know your opinions.

Thank you

 

[waltube]

I have seen the spec of the Nichicon and seems to be fine for the job.
The capacitors normally can have + 5% of tolerance on voltage so these stuff are good, in my opinion.
You have to check only the dimensions.
In my opinion if you reach the 220 +220 uF= 440 uF you will get a better results on all parameters.
The delay circuit takes about 5 secs and it is enough for inrush current.


Walter

 

[kodabmx]

Kodabmx thank you for the advice. Did you try it? Is it reliable?

I've used several and only ever had one failure. The 555 went bad but it was about 80c in the chassis that time.