Cold tubes in warm amp = smoke?

[tomchr]

If you have a schematic of the amp, the resistor value should be noted on the schematic. For example, 680R or 1k2 (680 ohm, 1.2 kOhm respectively). If no value is indicated on the schematic or you don't have a schematic, look at the resistor. It'll either have markings like I describe above, or have colored bands on it. The colored bands mark the value (Electronic color code - Wikipedia, the free encyclopedia).

Ensure that one end of the resistor is disconnected from the circuit, either by unplugging what connects to it, or by desoldering that end. It doesn't matter which end of the resistor is disconnected. Then set your multimeter to read resistance and select a range that is a step up from the resistance you expect to read. Connect one lead to each end of the resistor. Read the resistance on the meter.

So let's say the resistor is marked 1K0 5% (or brown-black-red-gold), your meter should read 1000 ohm +/- 5 %. Any value in the range of 950 .. 1050 ohm is "good".

If the resistor is good, solder it back in. If not, replace it.

Now... If the markings are burnt off and you don't have a schematic, you're in for a project. If you have one channel of the amp that works and another that doesn't, you can compare values between the two channels. If both channels are dead, you're hosed. Or, at least, you'll have to do a little design around the relevant section and figure a value that works.

Hope this helps.

~Tom

 

[bbogus]

Thank you VERY much! That does help.

 

[bayermar]

I might state the obvious, but just to be on the safe side (so don't get this the wrong way): If you have not looked at the sticky thread "Safety Practices,...", please do so before poking around in the amp. Always double check the amp is unplugged and caps are discharged, before starting your work.
Then follow Tom's advices. If anything is broken, I am sure you will be able to fix it easily - many members of this forum are VERY generous with their time and skills.

Best,
Martin

 

[speakerfritz]

the el-34's have a higher bias character so they will drain more current with 6l6 settings...if the current is too high....tube damage can result. Basically the amp set for 6l6's will need to be reset for el-34's using the bais adjust.

 

[bbogus]

the el-34's have a higher bias character so they will drain more current with 6l6 settings...if the current is too high....tube damage can result. Basically the amp set for 6l6's will need to be reset for el-34's using the bais adjust.

Strangesince the amp is rated to take both with no instruction to change anything on the bias. I'm sure there is a sticky for it . but how do you change the bias?

 

[tomchr]

If they're operating in pentode or UL modes, I would expect the 6L6 and EL34 to be interchangeable, assuming the heater circuit can handle the higher current of the EL34. For triode connection, however, the story is completely different. At least that's what I gather from looking at the plate curves in the respective datasheets.

~Tom

 

[vinylkid58]

Strangesince the amp is rated to take both with no instruction to change anything on the bias. I'm sure there is a sticky for it . but how do you change the bias?

It appears the amp is cathode biased, which means changing the cathode resistors on the output tubes is the only way.

Why not contact Garry @Musical Paradise directly with your questions? I'm sure he'd be more than happy to help.

jeff

 

[bbogus]

I have contacted Gary. Actually I sent him a link to this discussion. He says that I can use both and that the EL's will run hotter. But being a newbie both to this forum and to tube amps in general, I like to get many varied opinions.
I am learning a lot.