5E6A Bassman Build?

[ellum68]

This is my first post, so hi! After finishing a 5F2 a few years back, I've decided it might time to build something bigger and better. I'm a HUGE Luther Perkins fan (I took out the domain www.lutherperkins.com) and thought it would be kinda neat build a 4x10 Bassman like Luther used to use. I naturally assumed that his Bassman contained the famous 5F6A circuit until I noticed something in a picture I had. http://www.250r.us/luther/pics/2.jpg If you look closely at the back of his amp, I think you can just barely make out the twin rectifier setup of a 5E6A, not a 5F6A!

With that being noted, I'd like to build a 5E6A Bassman. I know Weber makes a kit, but it lacks a dual rectifer among other things that would make me pass on this kit. I've noticed that the 5E8A Low Power Twin shows strong similarities to a 5E6A Bassman. What advantage does the extra tube of the 5E8A offer? Say I did decide to stick a 5E8A into a 4x10 cab, what would I have to change to pull it off? I' ll probably be using Mercury iron. I know I will need a different output tranny, but am unsure of which one. Are there any multi-tap options? Do I just run the stock 5E8A power tranny? Which choke do I use? Last thing I noticed was different resistor just before the output jack. What dictates which resistor to use?

Sorry for the barrage of questions. I'm still very much learning about things. However, I know enough to work safely with 400v+ circuits!

[ellum68]

I got ahold of nice fella at Mercury and he set me straight o a few things. The only issue now is that Mojo's tranny opening on it's 5E8A chassis won't hold a Mercury Low Power Twin power tranny. Mercury suggested a 1958 Bassman. I hope the B+ isnt too high and that it will handle a dual rectifier.

[tubeswell]

The winding for the dual rectifier has to have 2 x the current-draw rating of a winding for a single rectifier. So 2 x 5U4G needs a 5V 6A winding.

Looks like that amp would want a High-Tension winding of about 345-0-345 rated @ 180mA or 200mA, and a heater winding of 6.3V (centre tapped) rated @ 4A or 5A.

[Diablo]

Leo's idea behind the dual rectifier (5U4GB) was to reduce voltage sag under load. The two tubes split the current so the voltage drop is less. In later designs, Leo used a single GZ34 rectifier, which is a low resistance tube, so it does the same thing as two 5U4GBs. Still later, he went to solid state diodes for even less sag. You can dial in the voltage sag yourself like Weber did with their copper cap rectifiers - it's a pair of silicon diodes with some large wattage resistors. Using two tube rectifiers, with all their heat generation, seems pretty pointless, other than for historical purposes.

[ellum68]

Diablo, you are correct in that my want for a dual rectifier is mainly historical. However, I have heard you can remove a rectifier to induce more sag. I'm not sure how much I would actually do that in practice though.

Tubeswell, THANK YOU for the information about the required heater draw. I e-mailed Mojo and asked about the opening in their chassis for the power tranny. They came back with...

Center to Center: 2 3/4 x 3 3/8
Opening size: 2 1/2 x 3 1/8

I then e-mailed Mercurcy Magnetics with my request....

Option 2:

5E6A Bassman driving a 4x10 8-ohm speakers for a 2-ohm load

Power Tranny: FTBP-58

Output Tranny: FO50BM-1

Choke: FC-2.84

Patrick advised using the '58 Bassman tranny as that's what would fit in the opening. I also got the spec sheet and that unit and noticed that it ain't gonna cut it as it can only give 3A on the rectifier draw. I also noticed it's going to give 380 - 0 -380, which seems a little a high. I could always do the zener diode on the center tap trick and use a single 5U4GB I guess. Or perhaps have the tranny opening machined for the proper FTBP-55 to begin with. I'm also a little curious as to why he advised using a 4-ohm blonde bassman output?!

I guess I have my doubts about trying to my hand at this. Although the challenge is kinda fun! I'm no guru by any means. Maybe I'd be better off trying to build a tried and true 5F6A.

[Diablo]

I took a look at the 5E6A schematic and you're correct, it looks very much like the 5E8A Tweed Twin. I would expect them to sound very similar. I've built the 5E8A and a 5F6A combos, and they sound much different from each other. If you can get a chance to listen to these two amps, it would be worth the effort, so you can decide which tone you like better. The two amps have distinctly different tone.

[ellum68]

How would you describe the difference in tone between the two? I play clean more than anything, like Johnny Cash, Scotty Moore, etc.

I did figure out something interesting about all the low power twin kits out there that I've seen. The power tranny opening is the same between the 5F6A and 5E8A chassis that are being made today. The "5E8A" chassis won't fit the correct low power twin tranny, so companies use the Bassman tranny instead. Both Mojo and Mercury list there Bassman tranny at 5v @ 3A. Sergio at Mercury said it would be fine, but it would bring the voltage down a bit. Seems like a fella would be better off machining the opening for the correct tranny or running a GZ34 instead and blocking off the extra octal hole.

[Diablo]

The 5E8A has more of a midrangey tone that overdrives more at lower volume. If you find a 5E8A or 5F6A to listen to, check out which preamp tubes they're using. Fender reissues use a 12AX7 rather than the 12AY7 (historically correct). The 12AX7 has a lot more gain. My 5E8A Weber chassis has the two octal holes for twin rectifier tubes. My plan was to try the amp out with one 5U4GB rectifier and if needed add a second rectifier later. I bought a 5V-3A transformer from Weber that is designed to power the heaters on a tube rectifier. However, I never added the second rectifier after playing the amp.

[Dagan8]

If a GZ34 will provide the same performance as 2 x 5U4G it might be worth the small change in aesthetics if it gives you more PT options.

[ES350]

I use a '56 5E8A and play with a pretty clean tone; swing, early country, etc. I use a single GZ34, NOS 7581A output tubes, the stock preamp tube compliment, and a pair of rebuilt and remagged P12N's; it's healthy. The 5E8A has the same PI as the 5E5A/5E7 etc, and will not stay clean in most modern settings (i.e. volume levels typically heard these days). If you want the big tweed cleans, go for the hi-power Twin or the 5F6A, both of which have the LTP PI. Luther did not have to contend with a drummer or an amped upright.

[dad love mom]

I use a '56 5E8A and play with a pretty clean tone; swing, early country, etc. I use a single GZ34, NOS 7581A output tubes, the stock preamp tube compliment, and a pair of rebuilt and remagged P12N's; it's healthy. The 5E8A has the same PI as the 5E5A/5E7 etc, and will not stay clean in most modern settings (i.e. volume levels typically heard these days). If you want the big tweed cleans, go for the hi-power Twin or the 5F6A, both of which have the LTP PI. Luther did not have to contend with a drummer or an amped upright.

Old thread, but a question for ES350 - Could you share your settings of your 5e8a? I'm trying to get a ballpark figure on how you set the amp and whatnot. Thanks. Also, did you have to do a specific and targeted bias of the power tubes when switching to a single GZ34? Thanks!