Happy Xmas day I am faultfinding on an amp, help!!

[stevesuk]

Hello Guys, haven't been around much, too busy at work and the amplifier building room/music room/den is virtually finished !!!

Due to too much alcohol on Xmas day I have decided to fault find on line !!

Anybody else getting away from the Turkey and mince pies ?

Problem - finished 36 watter with Ebay second hand power transformer.

NO B+

I have traced it down to (perhaps) the transformer not having a centre tapped HV out. It is 330V - 330V no centre tap. GZ34/5R4GY tried, intend using a Brimar 5R4GY to drop the voltage to a less valve lethal level.

I need to finish this amp before the 7th January when it is going to be used for recording an internationally released CD in a converted barn in Yorkshire. (think deep Louisiana) (can you believe these Virgin/HMV signed artistes !! ) I have told him he would be better off with a TMB 18 watt, but he just lurrrves the 36 Watt and wants one. Unless I steal one back from the people who are using my 36W builds. I am up S""t creek without a paddle.
The Artiste is a sort of ALT COUNTRY blagging Neil Young'ish with original numbers sort of thing

I don't have another suitably rated transformer, so I may revert to two old RS PTs in parallel, a trick I have used before. they are 250V 0V 250V and with 5V 3A, 6.3V 2A and 6.3V 1A.

So, the question is ? do you have to have a centre tapped HV output when using a GZ34/5R4GY or other 5V heater rectifier valve oops. sorry tube ?

Steve UK

[LeeMo]

Steve,
Merry Christmas!
If I'm thinking correctly, and I'm pretty much a novice, on Richie's layout in the gallery there is 290v above the center tap and 290 volts below the center tap which combine to give 540 volts AC. With no center tap on your trannie the voltage is 330 volts. If there were a center tap on that winding , it would have 165 volts on either side. Correct me if I'm wrong.


LeeMo
I have to go to Grannie's now. Good Luck!

[markd]

So, the question is ? do you have to have a centre tapped HV output when using a GZ34/5R4GY or other 5V heater rectifier valve oops. sorry tube ?
Steve UK

Hi Steve,
With a PT with no Center Tap on the High Voltage secondary, you will need to use a bridge rectifier. You can use the tube rectifier for two of the diodes in the bridge rectifier. Basically you will need to build a virtual ground from your tube rectifier to ground. Since a picture is worth a thousand words, I have attached a beautiful drawing below( OK it sucks, but it should give you the idea).
hth, markd

[Groundpath]

Hi Steve,
With a PT with no Center Tap on the High Voltage secondary, you will need to use a bridge rectifier. You can use the tube rectifier for two of the diodes in the bridge rectifier. Basically you will need to build a virtual ground from your tube rectifier to ground. Since a picture is worth a thousand words, I have attached a beautiful drawing below( OK it sucks, but it should give you the idea).
hth, markd[/quote]

Or run two rectifier Valves to make a full wave rectifier.

[stevesuk]

Thanks, Mark, Groundpath, Happy Christmas.

Now I have sobered up I can think back to Electrical Theory and visualise the two diode/CT transformer full wave trick. I have some IN4007 diodes somewhere, they will be in as soon as I find them.
Thanks again.
Steve UK

[LeeMo]

O.K. so they corrected me
At least I bumped it to the top again!


LeeMo