Bassman Ten

[Gone_Fishing]

I found an ole Bassman Ten fairly cheap. I want to convert it to 6550's. Here are my questions.

(1) Will the filament supply in the power transformer be able to supply the amperage they need, if I get a 3A auxiliary heater for the phase inverter and two preamp tubes?
     
      Or should I get a 6 to 10 amp auxiliary heater for the 6550's and use the PT heater supply for the three 9 pinners.

(2) Will I be able to use a Twin Reverb output transformer? (I want to use the original power transformer).

(3) Will insulating the cab with fiberglass batting help the tone? (I will get new/better speakers)

Thanks ahead for your help.

Gone Fishing

[smackoj]

Is this the amp you have?  Are you wanting to play bass thru it?

[Gone_Fishing]

Yes sir, that appears to be it.  I know that these amps were not much as bass amps (that's what I've read, anyway),  but I'm retired/disabled, it's a hobby and I'm just trying to improve on CBS's "nuttiness" and possibly make it a decent low powered bass amp.  I don't play bass, I'm a guitar hacker.  I enjoy this kind of stuff,,,it keeps me busy in my spare time which is pretty much when I'm awake now.

[Willabe]

Why 6550's?

Heater current;

6550; 1.8A each, 3.6A x 2
6L6GC; 0.9A each, 1.8A x 2
12 _ _ 7; 0.3A each, .9A x 3

Amp has 3 x 12 _ _ 7 = 0.9A and 2 x 6L6GC = 1.8A, so 2.7A total. If you go to 6550's, you need 1.8A more, 4.5A total.

Here's the link to the schemo in Doug's schematics library; 

http://el34world.com/charts/Schematics/files/fender/Fender_BASSMAN_10.pdf


                    Brad   

[smackoj]

I don't think that I would be trying to add any aux. heater transformers myself. I would probably just stay with the 6L6 tubes or you could try a pair of 7027a power tubes. The data sheet says they draw .9 amps per tube so that keeps you safer for your heater current draw. I have used these tubes in a bass amp and they sound very good.

A Twin Reverb OT could be useable but they are a high dollar item whether used or new and you may like the sound of the Bassman Ten enough without changing the OT. The Twin Rev. OT is designed for 4 output tubes so you would have to change the impedance of your speakers. I'm not sure whether the Bassman Ten has two spkrs. or ?  You may be satisfied with your OT after you install new speakers because using a higher quality speaker can make a huge difference.

I don't know it your Bassman Ten cabinet is closed back? If it is then adding some insulation should have a slight impact on projection of the notes but maybe not the 'tone' of your sound? If it is closed back and you open it up, make sure you get it back together without voids, gaps and rattles or you will be chasing cab noises which is a real PITA. 

 

revised: As senor Sluckey states in the next post, if you do decide to run a Twin Rev. OT, you will need to change the speaker load to 8 ohms. That's if the Twin normally runs into 4 ohms which I am not certain about. 

[sluckey]

I believe that using a 4 tube OT for 2 tubes requires you to attach a speaker load that is 1/2 of the OTs normal impedance. If the Twin Rev. is designed for a 4 ohm speaker load, then you would need a speaker that only has 2 ohms.

That's backwards. Two 6L6s into a TR OT would want to see an 8Ω speaker load.

[Ed_Chambley]

I found an ole Bassman Ten fairly cheap. I want to convert it to 6550's. Here are my questions.

(1) Will the filament supply in the power transformer be able to supply the amperage they need, if I get a 3A auxiliary heater for the phase inverter and two preamp tubes?
     
      Or should I get a 6 to 10 amp auxiliary heater for the 6550's and use the PT heater supply for the three 9 pinners.

(2) Will I be able to use a Twin Reverb output transformer? (I want to use the original power transformer).

(3) Will insulating the cab with fiberglass batting help the tone? (I will get new/better speakers)

Thanks ahead for your help.

Gone Fishing

The studio input is great for guitar providing you drop the preamp plate voltage to around 180v.  The normal is over 250v which makes it sound sterile IMO.

The ones I have messed with are closed back.  For Bass cabs I usually line the walls with 1" sound foam and spray glue.

I would use a separate filament transformer for all the tubes mainly because I already have one up to the job.  If I had to choose I would run the 6550 filaments separately.

The master volume is not a good design to me.  Sounds very thin.  Easy fix.

What is the HT ma?  I guessing the 6550 will pull down the voltage.  Will the iron run the 6550 and if so will it pull the voltage down so much you will not get any benefit from what you want to do.

I will say I have made nice sounding guitar amps from these and bought nothing.  Just rewire them like a Blackface Pro and add a different master volume.  The LarMar master works nice in a fender circuit.  You have to rework the Phase Splitter, but hey what is a few resistors.