You Vote: BOG EL34 vs. 6550

Tone-Freak · Post by **Tone-Freak** » Sun Nov 30, 2008 4:45 pm

Its not a super bass its a super lead the only thing changed is the split to shared and one cap

The amp was for sale once on ebay and i got the pictures from the ad

I cant remeber where I got the 10xxx gut shot though

Billy Batz · Post by **Billy Batz** » Sun Nov 30, 2008 5:29 pm

Tone-Freak wrote:Just curious where did you hear the Hendrix amp at the rock and roll hall of fame has 6550's in it I have never heard that before.

Is a 6550 the same as a 6L6 and can you just put them in and rebias or will there not be enough room on the bias pot

Years back some guy on plexi palace was there and sneaked a look. There wont be enough room on the bias pot. 6550s can take a really low -voltage. I literally have mine biased at like 100mA. They may not last as long but they dotn burn up. The other thing about that mod that tech claimed he did was changing the bias splitter resistors (220ks) to 100k. Thats right out of the book for changing marshalls to 6550. Its effect would be like having a post phase inverter master volume turned down slightly. To about 8ish. It would clean up the breakup a bit especially in the muddy low end.

Ive seen the guvnor before. I was blasted on another forum for saying Hendrix may have preferred chared cathode V1 when I first heard about the mod- back when I bought the Super Bass and really wanted to think that was it for BoG. "How do you know what Hendrix liked, and how would Hendrix even know what a cathode is'- yada yada. Obviously they miss the point. If the mod really was done Hendrix need not know what a cathode is. The tech he took it to and said 'Make it sound more like the old ones' would have been the one who knew. If that was what he thought he should do to the amp then you could easily imagine thats what Hendrix may have said to him.

Tone-Freak · Post by **Tone-Freak** » Sun Nov 30, 2008 5:44 pm

wouldn't making it shared clean it up also making it sound more like it had 6550's in it

Billy Batz · Post by **Billy Batz** » Sun Nov 30, 2008 5:48 pm

basile865 wrote:Interesting combination, shared cathode and a bright cap. Never heard about him having a favorite amp nick- named guvenor. That is essentially a super bass with a bright cap correct? Maybe that old super bass speculation has some truth to it dan.

On a side note, I wonder if marshall's pedal named the guv'nor has anything to do with that amp. Maybe an inside story to that.

Where did you learn about these two and get the gut shots, at the museum?

Those shots have been floating around for a number of years.

Putting a large bright cap on a Bass or JTM amp is a personal favorite. In fact using a 5000p cap at about 7ish can add some great aggressiveness to shared k marshalls.

Billy Batz · Post by **Billy Batz** » Sun Nov 30, 2008 5:49 pm

Tone-Freak wrote:wouldn't making it shared clean it up also making it sound more like it had 6550's in it

No. Shared cathode, if anything, sounds more gainy to me. More mid and low frequencies are boosted. Its a misconception because so many of the other 'lead mods' add gain. The purpose for that change could only be to make the bright channel brighter. I even have it on a switch on one amp, the one I use with 6550s coincidentally. The difference is negligible.

Amp building nuts like those of us here may get carried away describing mods but the fact is even a cathode bypass doesnt doesnt add or subtract all that much gain on its own. Not in a marshall. 2 preamp tubes really only amount to a simple 2 stage preamp. The first is in parallel the b side of the second is a buffer and with the tone stack it actually looses gain slightly.

Tone-Freak · Post by **Tone-Freak** » Sun Nov 30, 2008 7:16 pm

Billy Batz wrote:
Tone-Freak wrote:wouldn't making it shared clean it up also making it sound more like it had 6550's in it
No. Shared cathode, if anything, sounds more gainy to me. More mid and low frequencies are boosted. Its a misconception because so many of the other 'lead mods' add gain. The purpose for that change could only be to make the bright channel brighter. I even have it on a switch on one amp, the one I use with 6550s coincidentally. The difference is negligible.

Amp building nuts like those of us here may get carried away describing mods but the fact is even a cathode bypass doesnt doesnt add or subtract all that much gain on its own. Not in a marshall. 2 preamp tubes really only amount to a simple 2 stage preamp. The first is in parallel the b side of the second is a buffer and with the tone stack it actually looses gain slightly.

If shared to split does not make much gain or the .68V2 bypass cap either them why do split cathode amps have so much more gain than a super bass? The other differences .1 to .022 coupling and .1 to .022 only make it brighter.

Billy Batz · Post by **Billy Batz** » Sun Nov 30, 2008 9:22 pm

So much more gain? I wouldnt say that at all. And your missing a few differences.

Split/share
Brite cap
V1 normal coupler
Tone stack values
V2 Ck present or not
Output couplers
NFB

The Tone stack values and the NFB amount by far the most effect. The NFB amount in a 69 Lead and Bass would presumably be the same so you cant count that. The tone stack makes a large difference though. Then the presence or absence of a bypass cap on V2 but thats not a huge difference at all on its own. The thing I think has traditionally given people the impression of a significant gain difference is the brite cap on leads. Its so huge at 5000p when you dial in the amp anywhere except at or near 10- say 8.5ish to 10- it seems to blow away Basses with no cap or small values at the same volume setting. On ten that difference is gone but basses are really fuzzy on ten and I think a lot of people dont run them on 10.

But when you go from split to shared your not only increasing the bypass cap value (which increases the range of boost) but your decreasing the Rk. On paper you would think its a significant gain boost but its really not that audible. Slightly more saturated maybe.

Now if your talking about NFB changes like the difference between 66/67 JTM45/100 and JTM100 as compared to 69 1959s, than now your talking a bigger difference. Even then in the grand scheme of things its not what youd call a big difference but your not getting EVH from them.

Billy Batz · Post by **Billy Batz** » Sun Nov 30, 2008 9:36 pm

Here ya go

SW1 - Split/Share - the bright channel coupler is always on 22n because I like it like that

SW2 - 5000/none/500 brite cap
SW3 - .68/none/330u V2 Ck
SW4 - 33k/500p vs 56k/250p stack
SW5 - .022/.1 output couplers

I used to have a pot that changed the NFB resistor value from 10k to 110k. Its gone.

basile865 · Post by **basile865** » Sun Nov 30, 2008 10:27 pm

if I was to put in 6550's or KT88's would the drake 67 spec 2" OT not work?

Roe · Post by **Roe** » Mon Dec 01, 2008 5:51 am

the drake should work. perhaps you should consider lowering the 220k bias splitter resistors to 150k in order to prevent possible blocking distortion

basile865 · Post by **basile865** » Mon Dec 01, 2008 12:50 pm

Alright guys I recorded the best Who Know's I could muster with my stock EL34's. Too much gain IMO, and it wasn't even fully cranked. Has too much fuzz on top, in comparison to the actual who knows which has a much smoother gain.

Go to my reverbnation page listed in my sig and its the last song on the list "who knows."

Listening to that and then the actual who knows has a large difference in tone, which is the result of a lot of variables, but still it sounds like a diff tube characteristic. Let me know what your opinions are.

Billy Batz · Post by **Billy Batz** » Mon Dec 01, 2008 3:37 pm

Just as a disclaimer I understandf this is pure speculation.

If Im to keep running with my 6550 idea I think the fact that he did claim he changed the splitters to 100k (he did say 100k right and not 150k) would make a big difference because right now Im still getting a bit too much drive on 10. I may stick my PPIVMV back into that amp to be able to do that and put it back when I use EL34s. Of coarse if its not BS than having the high wattage speakers changes a lot as well.

basile865 · Post by **basile865** » Mon Dec 01, 2008 6:16 pm

Do you hear how fuzzy it is on top though? its totally not as smooth as the original who knows tone. His just has a hint of breakup smooth overdrive where mine is real fuzzy and farty.

JimiJames · Post by **JimiJames** » Mon Dec 01, 2008 8:25 pm

yeah I hear it.
What are the speakers again? G12T-75's?
If they are, I think there's where I would be looking to solve some of the tone.

FWIW I think it's good. It's when you roll on more volume the gain kicks in coming from the top. Couldn't that be tweaked?

basile865 · Post by **basile865** » Mon Dec 01, 2008 8:33 pm

yeah the speakers arent the greatest, but being that theyre 75 watters I'm assuming theyre only helping keep the amp cleaner than a lower wattage speaker. In which case there'd be even more gain.

Thats just straight amp nothing else you know? plus it wasnt cranked. So again, His sound was a good bit cleaner IMO.

I've got this fuzzy thing going on up top that I hate.

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