The Amp Garage

Here is the PT datasheet, I got the wrong one in the previous post. So the 300V secondaries show continuity to ground, is that as it should be??

IMG_2295.JPG Ok, redid the whole bias board today, see attachment. I checked for continuity to ground, and was surprised to get continuty beep from the yellow high voltage wires feeding the bias board. Is this expected, or does it indicate a fault in the PT? Haven't tried to power it up yet. I also...

Yes, M Fowler is right, and I did a continuity test on all the standoff screws. But anyway, this weekend I will disassemble the whole bias board and check all connections once more.

The bias board was originally soldered from below. Since the picture you annotated was taken, I have re-soldered all connections from above. I'll put up a new picture tomorrow.


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Replaced the bias caps today, but still I am getting 0 bias voltage, and only -9 VDC after D11. I then replaced R29 and D11, but nothing changed. The AC voltage before D11 is just under 600V. I am truly at a loss about what do try next, hopefully someone can point me in the right direction. Sent fro...

Does this one seem ok? 450V, but should be able to fit it onto the board.

http://www.tubeampdoctor.com/en/shop_Ca ... acitor_510

Sluckey wins the contest, C22 has 0 ohm resistance across the terminals. So I will replace it. Any particular cap I should choose, or just any generic 10uf 100V electrolytic cap?

Check for continuity to ground from the PCB trace wiring positive leads from two 10mF electrolytics. My guess is that it's floating. I have continuity to ground from the + side of those capacitors. Reflowed all solder joints in the bias circuit. Still -9V at the junction of C21 and R30, and 0V at t...

I get -9 V DC after D11. Before R29 and the rectifier diodes I have 598-600V AC, right at my meter's limit.

Measured R29 to 220k, as called for by the schematic. And R31 to 15k.

Could the bias capacitors be faulty, or the wrong value? They are marked 10mf 100V.

Please remove your power tubes. Power up and measure DC at pins 5 on the power tube sockets. That's where your negative bias voltage should be. Adjust the bias pot on the rear panel for maximum negative DC. You should be able to get -30 or -40ish volts. Hello Xtian, I went to ampgarage to get more ...

Hi Shipwreck: what are those 2 resistors under the yellow alligator clip? they kinda look like 1 ohms? which should be on pin 1 and 8 - to ground on the el34's and a connection to the bias test ports I just looked at the layout on the DIY forum, and didn't see any resistors where you have them ( un...

On the other sid of R30 I get -9 VDC, on the other side of R31 0V.

I get 0.0 voltage reading from the junction you mentioned to ground.

I get red-plating starting up with just the power tubes.

Some details on the build? Pictures would almost certainly help. You should be able to install just power tubes and bias up without red-plating. You neglected to include your bias circuit voltages. Best .. Ian[/quote] Thanks for the comments, I will put some pictures up shortly. I am fairly new to a...

Completed an Express with parts from rj guitars, and fired it up with tubes last night. The power tubes started redplating after around a minute, so had to turn it off quickly. Today I measured all the B+ voltages without tubes, here's what I got (allow for small discrepancies that could be the faul...