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Bugera 1960 power amp conversion - not anymore... 
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Location: Manchestoh, UK
jgreenwd wrote:
Zozobra wrote:
Good spot, thanks :)


:thu: I’d love to see an updated layout when you get it sorted. I’ve been toying with the idea of regulating the screens on a Fender’ish build.

What is your pass device? Are you sinking it to the chassis or something more substantial?


Turns out I just forgot to draw the underboard jump wire from the B+ to the 1k resistor :lol:

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Loop wrote:
I’m currently shopping for a 1996 Red Dodge Viper with yellow wheels. Who gives a shit about taste?!


Sun Nov 18, 2018 9:14 am
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First fire up of the power supply. Brought it up slowly on the variac with no problems or magic smoke escaping. 500VDC on the plate node and the MOSFET regulator is working spot on to deliver 400VDC to the screens and PI feed. Something isn't quite right with the bias supply but I'm outta time for tonight. Getting there :)

EDIT: bias sorted - it was just a cold solder joint. I'm going to need to bring the range down on it though as it's waaay overkill.

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Loop wrote:
I’m currently shopping for a 1996 Red Dodge Viper with yellow wheels. Who gives a shit about taste?!


Wed Nov 21, 2018 12:34 pm
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Adjusted the bias supply to a sensible range. We know that to get the tube to pretty much cut off we need a bias of:

-V_screen/µ_tube
or
-V_plate/10

KT88s have the lowest µ_tube of anything I'm likely to stick in at a value of 7.5. 6550s are slightly lower at 6.8 which isn't a great deal different. This means they'll need the largest range to bias up. In this case

V_bias = -400/7.5 = -53VDC or -500/10 = 50VDC

with the stock circuit I had something utterly ludicrous like -125VDC! To cull this I've added a resistor between the -ve output of the rectifier and the bias reservoir cap. In this case I used 47k, which forms a potential divider with the bias pot and the range protection diode to bring the raw bias down to a more sensible -60ish VDC. I need to tidy the wiring up after all this fudging around but the power supply stuff is done now.

Next up I need to wire up the power tubes and drill holes for the preamp tubes. After that I can get this thing making some noise.

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Loop wrote:
I’m currently shopping for a 1996 Red Dodge Viper with yellow wheels. Who gives a shit about taste?!


Thu Nov 22, 2018 12:15 pm
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