Bassman 6G6 pre amp questions
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Bassman 6G6 pre amp questions
Anyone know why the bass channel on the 6G6-A bassman was changed from the 5F6-A? It is an unusual layout using a 220k plate fed first triode followed by a CF, then TS without treble, then 2 more triode stages followed by treble. This seems like a big departure for Leo.
Re: Bassman 6G6 pre amp questions
Not sure why he changed it but it was common for Leo to make changes as he went along.
Many times he would walk out on the factory floor and tell the techs to make changes without documenting them.
Then later they would revise the schematics.
If it turned out that the mod was not good in the end, they would simply stop doing it but maybe 50 amps went out the door with it.
It drove everybody crazy because even though Leo was the CEO, there were others that managed their own departments.
Leo was known to be very frugal and he liked to use everything up before ordering new parts.
He would use up the old tube charts before dipping into the new ones to save a dime.
So a AA270 might actually be a AA371 circuit wise.
The techs would always have to look the amp over to figure out which schematic to follow.
Sorry for the derail and history lesson.
Many times he would walk out on the factory floor and tell the techs to make changes without documenting them.
Then later they would revise the schematics.
If it turned out that the mod was not good in the end, they would simply stop doing it but maybe 50 amps went out the door with it.
It drove everybody crazy because even though Leo was the CEO, there were others that managed their own departments.
Leo was known to be very frugal and he liked to use everything up before ordering new parts.
He would use up the old tube charts before dipping into the new ones to save a dime.
So a AA270 might actually be a AA371 circuit wise.
The techs would always have to look the amp over to figure out which schematic to follow.
Sorry for the derail and history lesson.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Bassman 6G6 pre amp questions
Didn't Marshall do the same thing with faceplates and whatnot?
Re: Bassman 6G6 pre amp questions
Well this model was an unusual departure which seems odd with hind sight that he moved away from the 5F6-A architecture in ths bass channel.
[img:998:688]http://www.turretboards.com/layouts_sch ... n_6g6a.gif[/img]
[img:998:688]http://www.turretboards.com/layouts_sch ... n_6g6a.gif[/img]
Re: Bassman 6G6 pre amp questions
While I wasn't there when Leo and cohorts were making the changes, I will offer a few guesses re this amp as I have a Bassman head:
On the 5F6, there is an input gain stage followed by a volume control, followed by a recovery stage and then a cathode follower-driven tonestack. Assuming it's the goal of most early (and present) bassists, we want a fairly clean sound. Lets say your bass instrument's low frequencies were distorting the recovery stage at a certain setting of the volume control (usually about 4-5). Unfortunately, with the late-stage tonestack you can't trim the offending frequencies to get a little more headroom so the amp's distortion point is your limiting factor as far as clean signal volume from the 5F6.
On the heads, the bass channel usually gives you a fairly "boomy" bass when used with a bass guitar. The first gain stage will be a bit brighter and tighter than the standard 100K/1.5K/25uF stage in the normal channel. The early stage cathode follower will help de-emphasize low frequency noise and hum through degenerative feedback. It also helps with the subsequent tone stack loading. There was probably significant tone stack loss (especially in the mids) resulting in the need for the two recovery gain stages after the tone stack. The tone control probably allowed for more dramatic cut than just a treble control a la the 5F6. Overall, this design gives you BIG bass, the ability to trim the bass early in the channel to allow a little more headroom and the ability to dull it down. Apparently, that muffled bass sound must have been quite popular as my head's bass channel was just mud until I re-worked it. However, it looks like this bass channel design would distort more than the "tighter" setup from an Ampeg made around the same time.
Just a guess. Hope I've helped at least a bit, BTF.
On the 5F6, there is an input gain stage followed by a volume control, followed by a recovery stage and then a cathode follower-driven tonestack. Assuming it's the goal of most early (and present) bassists, we want a fairly clean sound. Lets say your bass instrument's low frequencies were distorting the recovery stage at a certain setting of the volume control (usually about 4-5). Unfortunately, with the late-stage tonestack you can't trim the offending frequencies to get a little more headroom so the amp's distortion point is your limiting factor as far as clean signal volume from the 5F6.
On the heads, the bass channel usually gives you a fairly "boomy" bass when used with a bass guitar. The first gain stage will be a bit brighter and tighter than the standard 100K/1.5K/25uF stage in the normal channel. The early stage cathode follower will help de-emphasize low frequency noise and hum through degenerative feedback. It also helps with the subsequent tone stack loading. There was probably significant tone stack loss (especially in the mids) resulting in the need for the two recovery gain stages after the tone stack. The tone control probably allowed for more dramatic cut than just a treble control a la the 5F6. Overall, this design gives you BIG bass, the ability to trim the bass early in the channel to allow a little more headroom and the ability to dull it down. Apparently, that muffled bass sound must have been quite popular as my head's bass channel was just mud until I re-worked it. However, it looks like this bass channel design would distort more than the "tighter" setup from an Ampeg made around the same time.
Just a guess. Hope I've helped at least a bit, BTF.
Re: Bassman 6G6 pre amp questions
There is information on Hendrix using this 6G bassman on the track voodoo child revisited. He always used a Fuzz Face which was an important part but a Brown bassman head was used for recording.
Re: Bassman 6G6 pre amp questions
As a bassist, I can tell you I prefer the normal channel.
Re: Bassman 6G6 pre amp questions
I agree totally, 6G6. When I got my Bassman head in the early 80's, I tried the Bass channel and was very perplexed. I suppose the sound would be okay for those Gospel players who like a boomy, muffled sound (I know several who've never played bass without turning their bass tone controls completely to "0" 
). I threw collector's value to the wind and modded the bass channel with a preamp more appropriate to clearer bass and guitar.
). I threw collector's value to the wind and modded the bass channel with a preamp more appropriate to clearer bass and guitar.Re: Bassman 6G6 pre amp questions
I believe I read that Eddie Kramer said in his book that it was a blackface Bassman Hendrix used, which would be a aa864, that puts the tone stack between stages i.e. earlier than the 6g6. At least thats what I've heard I haven't read Kramer's book firsthand. (which is how internet lore goes) I can't substantiate that but only a handful of people in the room that night probably could for sure. *shrug*
Regards,
RD
Regards,
RD
Re: Bassman 6G6 pre amp questions
I wouldn't doubt that about his using the 864. I've also seen pictures of a BF Bassman in Lindsey Buckingham's studio. I don't know whether he uses it for bass or guitar.
I do know that if Hendrix used an 864, he was probably using the Normal channel unless he had it modified. I couldn't get anything remotely resembling a good tone out of my Bass channel before I modded it.
I do know that if Hendrix used an 864, he was probably using the Normal channel unless he had it modified. I couldn't get anything remotely resembling a good tone out of my Bass channel before I modded it.