# pulling tubes on a 4-6L6 Fender



## dwagar (Mar 6, 2006)

Wild Bill or other amp techs please:

A friend of mine has an old PA100 Fender head, 100 watts, 4 6L6s. He'd like to start using this as a guitar head.

I understand you can pull 2 tubes (eg the 2 outside tubes) to drop it to basically a 50 watt head. Will it start to break up earlier? 

Does this require a rebias? Or is it as simple as pulling 2 tubes?

and I've read that you have to change it from 4 ohm impedance to 8 ohm. Then I assume you need an 8 ohm cab to match it to? Or, if you are running into an 8 ohm cab, do you set the head then to 16 ohms? This has me a tad confused.


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## Wild Bill (May 3, 2006)

dwagar said:


> Wild Bill or other amp techs please:
> 
> A friend of mine has an old PA100 Fender head, 100 watts, 4 6L6s. He'd like to start using this as a guitar head.
> 
> ...


Not hard, DW! Pull either the inside or the outside pair. Don't take them both from the same side.

Don't worry about the bias. It doesn't change. The voltage will be there at the socket for any tube that needs it.

As for the impedance, although tubes are tough enough to not care a lot you should give 'em a bit of a break and put an 8 ohm speaker on the 4 ohm output, or a 16 ohm onto an 8.

This is because when you pull two tubes the proper load at the plates of the tubes is now doubled. This means that in order for the output tranny to convert the speaker load up to the plate load you have to move the speaker down a tap. This will double the ratio through the OT.

Hope this helps!

:food-smiley-004:


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## NB-SK (Jul 28, 2007)

Wild Bill said:


> Not hard, DW! Pull either the inside or the outside pair. Don't take them both from the same side.
> 
> Don't worry about the bias. It doesn't change. The voltage will be there at the socket for any tube that needs it.
> 
> ...


This gives me an idea. I've got 2 WGS British Leads and 2 V-30. I could load one of each in the combo, then make an extension cab for each of the other two speakers and use them when I pull out 2 tubes. This would give me maximum versatility..Then again, I'm sure you'll recommend that I save the lumber and simply disconnect a speaker, keeping whichever of the two that I want to use connected.


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## dwagar (Mar 6, 2006)

Thanks Bill!

I'll have a chance to play around with it on Sunday.


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## dwagar (Mar 6, 2006)

hey, it worked like a charm.

next question:

the PI is running a 12AT7; will switching to a 12AX7 dirty it up just a tad?


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## Adicted to Tubes (Mar 5, 2006)

Not worth the effort to swap the PI tube.there are lots of other ways to dirty things up.Like remove the negative feedback wire on the output jack.

www.claramps.com


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## dwagar (Mar 6, 2006)

great thanks for the input.

I've just sent your link to my buddy, told him to give you a call when he has time to discuss what mods might work best for what he's trying to accomplish. It's great that you are local.


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## hollowbody (Jan 15, 2008)

Wild Bill said:


> As for the impedance, although tubes are tough enough to not care a lot you should give 'em a bit of a break and put an 8 ohm speaker on the 4 ohm output, or a 16 ohm onto an 8.
> 
> This is because when you pull two tubes the proper load at the plates of the tubes is now doubled. This means that in order for the output tranny to convert the speaker load up to the plate load you have to move the speaker down a tap. This will double the ratio through the OT.


How does this work for a combo amp? I have a Traynor YGL-3 that I would like to try this on, but as far as I recall, it doesn't have separate impedance jacks to run the signal from.


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## Wild Bill (May 3, 2006)

hollowbody said:


> How does this work for a combo amp? I have a Traynor YGL-3 that I would like to try this on, but as far as I recall, it doesn't have separate impedance jacks to run the signal from.



Well, you can't do nuthin'!:smile:

Just live with the mismatch. The Traynor is a tough amp and will laugh off any such "girly man" issues!

:food-smiley-004:


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## hollowbody (Jan 15, 2008)

Wild Bill said:


> Well, you can't do nuthin'!:smile:
> 
> Just live with the mismatch. The Traynor is a tough amp and will laugh off any such "girly man" issues!
> 
> :food-smiley-004:


Haha, awesome! If I somehow blow it up, I'll drive it up to you to fix for me! :banana:


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## Jim Jones (Sep 18, 2006)

Adicted to Tubes said:


> Not worth the effort to swap the PI tube.there are lots of other ways to dirty things up.Like remove the negative feedback wire on the output jack.
> 
> www.claramps.com


I don't think I agree with that statement at all. Disconnect the feedback if you like splatty, ragged overdrive, sure. Hardly less effort to do that than swap a tube.

Jim


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