pulling 2 tubes in a dual showman?

[Mike7]

Had a problem with a loose tube and it was correctly diagnosed here to be a loose pin #5. Unfortunately once again I'm having the same problem, can't really afford to replace the socket at the moment so I pulled the two middle power tubes and ran it with just two. I can only say that the sound was great, not as powerful and clean as running all four but kinda like that Fillmore East tone if you know what I mean. Anyway my question is can I keep running my amp with just two power tubes or am I slowly, or quickly for that matter, bringing it to a certain demise that will cost me much more than just putting in my tube holders that cost me $8 ?

[GearHeadFred]

I don't know about the Showman specifically, but if it's like many Fender 4-6L6 (I'm 99% sure it is - someone here will know), it's no problem. You're cutting the output power in half - which reduces the headroom and causes ealier breakup in the amp (good for some - bad for others!), and you have induced an impedance mis-match in the output transformer, which MIGHT cause it to work harder... but since you've also reduced the power, it's not really an issue.

[John Phillips]

It will cause the remaining tubes to work harder, but not the transformer which is under roughly half the stress it was, due to the lower power output. Don't run an extension cab as well as the main one when doing this, or you'll probably fry the tubes fairly quickly.

If the pin 5 contact is loose, you can re-tension it without replacing the socket. If it's not a loose pin contact but a broken grid-stopper resistor (common with old Fenders) it's easy and cheap to replace too. It would be only if the pin itself was actually broken that you would need to replace the socket.

[KevinOConnor]

Hi Guys

Tubes are "lazy" and will not work any harder than they have to.

In your Showman - or ANY fixed biased amp - you can pull tubes without worry and the remaining tubes WILL NOT WORK HARDER.

If you like the sound, you can operate the amp this way indefinitely.

You can extend this rufther and pull three tubes - or one tube from a two-tube output stage - and run that indefinitely, too.

This all falls within tube safety rules. Note that what most people follow are HIFI rules - but most are unaware of that fact.

Have fun
Kevin O'Connor

[Lolaviola]

Running the Showman w/ 2 tubes is doubling the Ohmage in the output.
If you normally run an 8 ohm load, it should match up, but if you run a 4 ohm cab, the amp now wants to see 8. So this will make the tubes "work" harder and may shorten their life. It gives a little different sound. The amp will be fine.

[jay42]

In your Showman - or ANY fixed biased amp - you can pull tubes without worry and the remaining tubes WILL NOT WORK HARDER.Go get him Phillips....okay, I'll try.

Kevin -- perhaps it's quibling...what happens to B+ when you pull these two tubes? What happens to the bias voltage when you pull these two tubes? Isn't the net effect that you're running the remaining tubes at a hotter bias relative to B+?

Note to the original poster...you can replace the contacts in a tube socket. The trouble is finding a sacrificial socket with the same style pins. Do try to tighten it first though.

[edit]hmm...no response...does that mean I win?