Fender Bassman Head 6G6-B circuit conversion

[tonefiend]

Hello,

I just came into a Blonde 1962 Fender Bassman 6G6-B circuit Head, and 2x12 cabinet. It appears this circuit was modded to add 2 more 6l6gc tubes? I am goin to embark on a project
to restore back to 2 6l6gc tubes and was hoping to get some help in how to remove the 2 "extra" 6l6 tubes to bring it back to factory. The Tube chart in the Amp shows 2 5881 tubes in the
power section. and 4 7025s in the pre-amp. Im guessing the owner wanted to make it 100 watt?

I will take pictures of the inside of the Chassis, and am hoping I can get some tips on how to remove the extra 6l6gc tubes.

Im going to post pictures of the inside of the Amp, as well as the schematic for a Fender Bassman 6G6B. I cant however seem to find where the attachment button is to upload the schematic.

Pictures soon to follow.

I was wondering if anyone could outling the steps involved in removing the 2 extra power tubes. Thanks very much in advance for your help.

[Enzo]

Look just below where it says Write Something. CLick the Upload Attachments button.

Removing the two extra tubes is easy...unplug them and set them aside.

Adding tubes does not make an amp twice as powerful. All the tubes do is transfer power from the power supply, so unless they upgraded the power transformer too, there is no extra 50 watts to add to the original 50.

SO before we can help you, you need to determine how far off stock the thing is anyway. What part numbers are on your power and output transformers? For all we know they are stock already. And if so, you literally need only just remove the extra tubes. The amp will not care if the two sockets are empty.


5881 and 6L6 are the same thing these days. Unless you are using antique real 5881 or something. In either case this amp would not stress either 5881 or 6L6.

And 7025 is just a special 12AX7, and today there is no difference to concern.

[tonefiend]

Thanks for the Reply Enzo,

Very strange I do not see an upload attachments button anywhere under "Write Something" Maybe its a browser issue, I am running Chrome however. at the bottom I see
3 buttons. Cancel, Preview, Post Reply and that is all. I do see how to upload pics by clicking on the camera icon, I will post pics tomorrow.

I will post pictures when I can of the inside of the Chassis. I will get the serial #s off of the Transformers and post them, I think they are stock. That would
be great if I can just pull 2 tubes.

Im still confused as to why you would want to add 2 more 6l6 tubes, if it has not effect?

Thanks very much for your help, im really looking forward to this project.

[Enzo]

Im still confused as to why you would want to add 2 more 6l6 tubes, if it has not effect?

Because they assumed it did work that way. MAny people assume that.

You only have 27 posts, sometimes they limit new members until they have been here a little while.

[Greg_L]

I'm very interested in this. I'm about to build a 6G6B myself. I can't imagine why anyone would mod one like that!

[Jon Snell]

Remove the extra 6l6s and that is it.
You can stick an adhesive paper circle over the now unused valve base if you want.

[tonefiend]

Here are some pics. Looks like the PT is original? It is stamped Fender if you look closely at the pic.

In the Pic of the additional tube sockets, the Red Arrow points to a wire connecting to the PT wire to Pin 1 on the socket.


Here is my to do list:

1. Clean the inside of the chassis
2. Im going to install a 3 prong power chord and get rid of the Death cap.
3. Replace the filter Caps
4. Make sure resistors have not drifted, and replace those that have.
5. Replace the the Grid Resistors with 2 Watt metal film on the power tubes.
6. Clean pots/jacks/tube sockets tighten things up.


Does anyone have a recomendation for number 1. on the list.

Will definately need help on .number 2.


thanks everyone for your help in this restoration project. I will also be uploading more pics based on what I am currently working on.

[dstrat]

looks like a Twin OT to me and according to that 022889.

[tonefiend]

According to the part number on the PT this IS a 100 watt PT. The part number = 022889 stamped on the Transformer (see pic) After a google search for that Transformer part number I came up
with this: http://www.classictone.net/40-18012.html


Can I still pull both tubes? OR does something else need to be done to bring it back to stock?

[Enzo]

Just pull the tubes and see what it sounds like.

[Helmholtz]

According to the part number on the PT this IS a 100 watt PT. The part number = 022889 stamped on the Transformer (see pic) After a google search for that Transformer part number I came up
with this: http://www.classictone.net/40-18012.html


Can I still pull both tubes? OR does something else need to be done to bring it back to stock?

As dstrat wrote it is an 80W/4Ohm OT (not PT).
Probably 2.2k/4 ratio. No problem to use it with 2 tubes but speaker impedance should be 8Ohm.

Is the PT original?

[tonefiend]

Just pull the tubes and see what it sounds like.

Do you have to pull certain tubes because its push/pull or can I pull any 2 Tubes? does the bias have to be changed?

[tonefiend]

As dstrat wrote it is an 80W/4Ohm OT (not PT).
Probably 2.2k/4 ratio. No problem to use it with 2 tubes but speaker impedance should be 8Ohm.

Is the PT original?

Oops sorry for the mix up in my Transformer terminoloy.

Yes, the PT is Original, 125P7a is the part number.

[Jon Snell]

Usually they are in pairs, ensure you choose one from each side.
Without a photo of underneath, it is a job to say but from your description, the outside ones are probably the extra valves.

[Helmholtz]

Looking at the picture, the 2 closely spaced tube sockets above the PT are not original. Doesn't mean you can just pull these tubes as the the original sockets seem to have been rewired for parallel operation.
I would find the original chassis layout and restore original wiring.