Classic 30 No preamp tube power - help debug!

[turnipfarmfx]

Well, I really did something stupid. Swapped out all my tubes but installed them backwards s in tubes 1-7 were put in 7-1. I know, I know.... Turned on saw a bright flash. Immediately turned it off. Realized what a dummy I was. Replaced the blown 1a fuse. Other checked out fine. Powered it back up and still no luck. Power amp tubes are glowing. Pres are out. Checked voltages and I am getting 130 volts at the fuse and around 370v for b+ and b++.

Any advice on what to check or swap out would be greatly appreciated. Thanks!

http://www.bustedgear.com/images/sch...classic-30.pdf

[Chuck H]

If you're really lucky you only blew a tube or something in the preamp tube filament circuit. The preamp tube filaments are in series so if one tube filament is bad none will light up. Try KNOWN GOOD tubes in the preamp and see what happens. If the old ones were "working" before the swap you can use those. If that doesn't work you'll need to open it up for some checking and testing. No way to know that the power tubes are ok either. We only know that they light up which means none of the power tubes has a blown filament.

[Enzo]

Get out your ohm meter and verify each preamp tube still has continuity between pins 4 and 5. When you plugged them into the EL84 sockets, you put 300v across the heaters. They may be burnt out.

Then check the power source. They are wired in series across 36v - three 12v tubes in series is 36v of heater. SO make sure the -36v is present. Make sure 15 ohm 5w R66 is not open, and do you have -36v at each end? Verify -36v is on pin 5 of V3.

[turnipfarmfx]

Thanks guys. Continuity exists between pins on tubes.. Verified voltage at both pins of resistor(-42.4/-41.6) and pin 5 of v3 (41.6)

[turnipfarmfx]

v3
1 - 373v
2 - -15mv
3 - -16mv
4 - 7mv
5 - -41.5v
6 - 373v
7 - 7mv
8 -0
9 - 190mv

without tubes in.

[Chuck H]

If you look at the schem (and BTW, thank you for attaching the schem to your post) you can trace the filament circuit from tube to tube. Check for continuity from pin 4 of one socket to pin 5 of the next, repeat, socket to socket. I can't tell definitively from the schematic which tubes are series-ed to which but it'll probably make itself obvious in the checking. You should be able to find a path that places all the preamp tubes in series without interruption.

[turnipfarmfx]

One of the replacement 12ax7 was also bad. Some luck. Thanks fellas. Learned a bit in the process.

[Chuck H]

One of the replacement 12ax7 was also bad. Some luck. Thanks fellas. Learned a bit in the process.

That's become a problem lately. You can't trust new tubes out of the box. That's why I stipulated "known good tubes". Tall order, I know. It assumes anyone in particular has spares that have been tested.