Deluxe Reverb RI - No current

[lowell]

This amp has a very audible hum... not the 60hz type. I swapped power and rectifier tubes w/ new JJs. I pulled PI just to be sure this was a power amp problem. Voltages on power tubes plates and screens are reading low: 350v (schematic says 391v). The grids are at the specified -39v. Cathodes are indeed grounded and all tubes are lit. The 5AR4 rectifier tube reads 354VDC output and there is 321VAC on input of rectifier. When checking bias on the tubes and adjusting bias pot I get 0-4.5ma on BOTH tubes. Clearly this is a problem. I've checked the bias circuit and I get -35 to -50 as the pot is rotated to either end. I'm at a loss here.

[Amp Kat]

Sounds crazy but you could still have a bad tube out of box failure. Did you check your screen resistors and make sure they read 470 ohms. Try pulling the power tubes and see if your voltage goes up and try patching a cord from send to return then try running into another amp from send out and run a signal to the return and see what you get. Test points 37 and 38 show 174 VAC ? Test points 34 & 35 show 22 VAC ? You should also check for the +68 vdc at the Cathode of the PI. Could be a cold solder joint in the output section if the preamp checks ok. If the tube is not pulling current and the bias is normal around -38 then something is open. It is possible you have a bad OT so ohm out (of course power down ) from blue to brown for around 50 to 100 ohms and from red to brown and red to blue for half of that to ensure your tranny is good.

[lowell]

Thanks Amp Kat. I was thinking the only thing left is a bad OT... would that botch current draw in power tubes though?

[Amp Kat]

Yes it could if it's shorted and the ohms test would show that. You can do the ohm test in circuit easily once you find the red blue and brown or just find the red and go from that to pin 3 of each socket.

[lowell]

i'll check it out Monday and report back... thanks!

[lowell]

Ok the OT measures 400ohms end-end and 200 from CT to either end....?????

[pdf64]

Are your B+ filter caps good, or even connected? What's the Vac ripple on the B+?

[lowell]

pdf64... you got a point there. I just checked and there is 70VAC on plates of power tubes and 52VAC on B+. I'm guessing this means the caps are bad? I checked and all is connected right.

[pdf64]

I'd be looking at the checking continuity of the wiring connections between the B+ node inside the chassis and the caps in the doghouse. The ripple is so bad that I think that they are not connected, rather than that they have gone bad. Remember the ground returns as well as the +ve line. Peter.

[lowell]

peter yes I checked all the continuity there and it's connected... will replace caps and see.

[lowell]

I pulled the lower of the 2 filter caps on the B+ and it was testing pretty poorly using the 9v battery tester. I put a new one in and VOILA! Thanks for the suggestions all.