Have I killed my output tranny?

[Bluefinger]

I think I know what I did ... I bet that tranny is fine. I was laying awake last night because I had a feeling that I have messed up something else ... and then it dawned on me ... I was so focused on that tranny that I completely forgot that I also rewired the presence control. The presence control did not work so I tried to wire it like the presence pot of a 5E5 or 5F4 (https://taweber.powweb.com/store/5f4_layout.jpg). I did not take into consideration that the first grid of V3 in a 5F6 type PI is grounded through the presence pot. I disconnected the grid leak!!!! I haven't had a chance to try it yet but that must be it!!!

I still don't know why that presence control was completely useless the way it was wired before but that's a different issue ...

[kg]

There is a reason they are in sockets.

I've read somewhere that the chance of damaging an OT is significantly less with no input signal - if I remember correctly you might run the amp way longer than 10-20 sec. without damaging it - could the experts in this forum please verify -
I mean in that case the fault might be something else.

with no input signal, the amp may be run indefinitely with no load attached.

[Pat Burke]

I came up with a test similar to the battery and neon bulb test mentioned above. Unplug and discharge the amp. Put a couple of clip leads on a healthy 9V battery. With the speaker connected, clip onto one end of the OT and "scratch" the other end. If everything is good you get a noise through the speaker comparable to directly testing a speaker with a battery. It's a quick go/no-go test of everything after the power tubes. Does anyone see any pitfalls to this test (other than the obvious need to be SURE the filters are discharged)?

Bluefinger, in case it's not the Presence control: Maybe I missed it, but did you check/swap the speaker and cable?

[Pat Burke]

[QUOTE=Pat Burke;206809]Does anyone see any pitfalls to this test (other than the obvious need to be SURE the filters are discharged)?QUOTE]

OK, I'm going to answer my own question. Scoping plate to plate on my 50W Marshall, it's no problem when the speaker is hooked up. But without a load, I get a spike of 800-900V. If you briefly make the connection, it's not nearly so much (maybe 300V), but if you leave it connected long enough to really build up the field it's huge.

It's more reasonable with a 1.5V battery (~300V with no load). Doesn't make as much noise through the speaker, but it's quite usable.

Kind of a graphic illustration of what can happen when you lose your speaker load.

[Bluefinger]

Yup, speaker cable is alread ruled out .. tomorrow morning I will be in the workshop again, then I'll know more.

[Bluefinger]

ok, it was the presence pot of course. Everything is working fine now and the amp sounds great. Thanks everybody for your help tho!!!

BTW ... the reason why that presence control didn't work in the first place was because I dumped the global feedback resistor ... but a 5F6 presence controll needs it to work propperly. stupid me ...