Howdy!
I'm replacing the output transformer on my 65 Fender Super Reverb. Ive settled on the Hammond 1650NA. Now, the curios thing is that Hammond mentions it having 40% screen-grid taps on the primary for Ultra-Linear operation. Now, I'm a beginner, but I know Fender=Awesome clean amp and Ultra-Linear=Hi-fi and Hi-fi=Super clean (duh), and I was wondering how I could incorporate this into my amp. I'm pretty handy at working on old fenders, so I can probably handle any wiring required.
I've poked around an old Mullard 5-20 schematic and I can see how these taps are incorporated, I'm really just wondering if these are feasible in a Fender.
I'm replacing the output transformer on my 65 Fender Super Reverb. Ive settled on the Hammond 1650NA. Now, the curios thing is that Hammond mentions it having 40% screen-grid taps on the primary for Ultra-Linear operation. Now, I'm a beginner, but I know Fender=Awesome clean amp and Ultra-Linear=Hi-fi and Hi-fi=Super clean (duh), and I was wondering how I could incorporate this into my amp. I'm pretty handy at working on old fenders, so I can probably handle any wiring required.
I've poked around an old Mullard 5-20 schematic and I can see how these taps are incorporated, I'm really just wondering if these are feasible in a Fender.
Guitarist who claim to have heard both are almost unanimous that the UL approach is less desirable when using the amp for guitar. Is the OP tranny intended to be used on either design?
The UL used SS rectification with no choke. The “normal” ones used tube rectification and a choke.
Schematic for the UL model shows 470ohmers on the screens. Same as with the non-ULs including the original 1965 and the reissue.
Reissue:
http://www.schematicheaven.com/fenderamps/65_super_reverb.pdf
Original 1965
http://www.schematicheaven.com/fenderamps/super_reverb_ab763_schem.pdf
UL
http://www.schematicheaven.com/fenderamps/cbs_70w_mstrvol_pullsw_super-pro-bmstr_rev.pdf
The UL used SS rectification with no choke. The “normal” ones used tube rectification and a choke.
Schematic for the UL model shows 470ohmers on the screens. Same as with the non-ULs including the original 1965 and the reissue.
Reissue:
http://www.schematicheaven.com/fenderamps/65_super_reverb.pdf
Original 1965
http://www.schematicheaven.com/fenderamps/super_reverb_ab763_schem.pdf
UL
http://www.schematicheaven.com/fenderamps/cbs_70w_mstrvol_pullsw_super-pro-bmstr_rev.pdf
Honestly I doubt you would like the sound. The Fender "clean" tone is really not all that clean. It has lots of harmonics and color. Try taking an electric guitar and recording it directly into a computer and you will see the direction that ultra linear will bring your tone. A truly clean tone - an electric guitar running direct into some hifi speakers - will sound very thin and bland.
oldmanStrat said:
Disconnect the pre-existing screen grid supply from the screen grids (pin 4 usually). (Easy enough to just remove the old 470R or 1k screen resistors that are often wired right on the socket)
Connect the transformer UL taps to the screen grids (In the same way that you would connect the anode connections to the anodes really... You sure you're pretty handy at this, you've asked a very simple question?)
Merlinb said:
I will readily admit that my modding of Fenders is based entirely off of basic stuff. I generally work with the eq and preamp stages, and I occasionally convert the power stage to use 6CA7s. I've never dealt with a true tube Hi-fi circuit, so my understanding of the ultralinear designs in them is next to nil. I was really just worried if the values of the screen grid resistors would change, or something along those lines. I'll give this a try. Who knows, I could make it a dandy new monoblock...
On ANY 6L6GC Output Fender you should change those 470 Ohm 2 Watt Carbon screen resistors to 1K 5W wire wound. The old 470 Ohm resistors often change their values quite considerably and after a bias failure are often open circuit. I've even seen them looking fine by a quick visual inspection but have had them fall out in 2 pieces when unsoldered to do the upgrade to 1K 5W. They can also be the source of quite a bit of "snap, crackle and pop" noise.
If using Ultralinear DO leave the screen resistors in place between the screen and the Ultralinear transformer connections.
Cheers,
Ian
If using Ultralinear DO leave the screen resistors in place between the screen and the Ultralinear transformer connections.
Cheers,
Ian
I've got a feeling that's not going to work...
Well, the UL doesn't clean up the preamps, only the power amp. And at that only within the power tube stage. it won;t cure imbalance in the phase inverter or something.
The Seymour Duncan convertibles were UL, the old Sunn amps were as well. There is plenty of precedent for UL guitar amps that sounded just fine. Such a conversion won;t change your fender Twin into a hifi.
The main argument against them in guitar amps - from a manufacturer's point of view - is that the extra taps in the output transformer cost more than a couple screen resistors.
The Seymour Duncan convertibles were UL, the old Sunn amps were as well. There is plenty of precedent for UL guitar amps that sounded just fine. Such a conversion won;t change your fender Twin into a hifi.
The main argument against them in guitar amps - from a manufacturer's point of view - is that the extra taps in the output transformer cost more than a couple screen resistors.
OrganicBud said:
Some bum I saw had a frankenchamp made so he could switch between triode and pentode mode by reconnecting the screen as the "anode". I dunno. If that isnt the way, then what would be?
It is the right way to fry screen grids of your tubes turning them into triodes permanently. However, fried wires from screen grids can short tubes inside making them absolutely dead. Dead tubes can damage your new output transformer and some other parts as well.
Anodes must stay connected always. You may use 2 pole-3 position rotary switch. In triode position connect screen grids (through 1K 5W resistors that must be soldered permanently to screen grid taps on tube sockets) to anodes (of the same tube!); in UL mode connect them to 40% taps of your transformer (of the same tube!); in pentode mode connect them to B+, where they were before modification.
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