Kendrick 5F6A extra gain stage

[smokebreak2]

I scored an early 90's Kendrick 2x10 Bassman recently, and have been tweaking it to taste.
I replaced the black frame speakers as there was a weird brightness I just couldn't dial out, after weeks of stage use.
I went with a Fat Jimmy ceramic and a 1028K(essentially the emi blue frames in the original RI)
I changed the PI entrance to 4n7 as there's just too much low end in the amp, and it sounds pretty darn good now. It likes a 12ax7 in v1, and has the 56K/.022/.022 tonestack. I also dropped the voltage in the preamp as the amp was a bit strident.

Amp sounds pretty darn good now, and now I'm onto this odd little feature the amp has...there is an extra gain stage, switchable via relay on the back, as well as a MV control on the back.
The thing is, the extra stage is between the Tone stack and the CF stages.

I've attached the original as it was originally designed, then 2 things I have tried. The original just didn't sound that good, kind of weird. #1 was meh, and #2 is pretty cool. I know this sound silly, but it sounds like what I think about when I think of a tweed amp almost cranked(but at much lower volumes)...as opposed to the beautiful cleans of a bassman till it's cranked. I just never play that loud anymore, which is why I'm looking to get that sound at reasonable volumes.

I wondering what you all think about ideas for gain stages in this spot. It seems I remember seeing an amp that did this a long time ago, maybe a Lee Jackson?? I can't remember, but would love to hear y'alls ideas.

Happy holidays - Jeremy

[Stevem]

To lower the DBs and still run the amp closer to its wide open sweet spot why don’t you just run thru one of the speakers .

If that’s better but you don’t quite have enough clean head room then make a whole new baffle for a 12” driver that has a higher DB rating then either of your 10” drivers.

All this being said I think your beating a dead Horse because your missing the main problem hindering you from getting completely what you want.

This is the fact that the amp only has one tone stack that your fighting to average it out to work the best for clean tones and what you want for your over driven tones.

The way I look at it is that the extra gain stage that can be switched in is a crutch.
Kendrick was trying to keep the amp as close to the old tweed version as he could while appealing to players current needs of higher gain for solo usage.

With the duel tone stack it falls short in filling that need.

If you really are all in for giving the time input to max out a one tone stack amp, then what’s your cost for this time input as compared with the added expense of a bit lesser built amp, but one with two channels and two tone stacks to tweak to get you 100% of what you want.

Just some food for thought here.

[martin manning]

...there is an extra gain stage, switchable via relay on the back, as well as a MV control on the back.
The thing is, the extra stage is between the Tone stack and the CF stages.

This was originally an FX loop, I believe. Is there a CF followed by a recovery stage post-tone stack that feeds the PI?

Your config 3 has the lowest gain, lowest plate voltage, warmest bias, and the most bass roll-off. The original was super wide BW, more than needed.

[LOUDthud]

I've never seen a schematic of the whole amp. Wasn't there an effects loop and a big old toggle switch in there somewhere ?

The Kendrick OT probably only has the 2 Ohm output.

[smokebreak2]

Martin, my bad I misspoke , I meant to say that the extra stage was after the CF driven stack and before the PI entrance.
It is indeed an fx loop, and the extra stage comes after the return jack. I guess it was marketed as "can also be used as an extra gain stage" sort of thing.
Of course it can, but it just didn't sound good, as I believe its true function was to recover from the loop
The guy I bought it from bought it from Gerald off the floor of the Dallas guitar show in '91 or so, and apparently Gerald told him that double function, as that's what he told me also.
Actually, now that I think about it, he didn't even mention the loop..Anyways...

Yep there's a big ol switch on the back, labeled " +" and "-".
It's built like a tank. I almost forgot, when I was trying out the amp it started making bad sounds. I flipped it over and one of the output tubes was redplating.
I still bought it and when I got it home saw that one of the legs of the bias trimmer had come loose

I'm just goofin around with my new amp as far as modifying it, I'm sure I'll just stick a pedal in front of it, but the reason I posted was because I realized that having a gain stage post tone stack in a Marshall type design, as far as topology goes, seems to be rare. To play my own devil's advocate, there's plenty of gain stages after the stack in a boogie, or Dumble, so why does it seem so difficult to design one for Marshall topology?

In short, is it just impossible to try and put a gain stage between the TS and PI and get a JCM800 sounding amp? I actually have an unused triode in the amp as well!


PS I'm pretty sure the OT sec is 4ohm, I can't remember how, I mustve put a meter on the speakers before I boxed them...

[pdf64]

Consider the Hot Rod Deluxe https://el34world.com/charts/Schematics ... deluxe.pdf
V1 sections are prior to the tone stack, V2 sections are after, all in cascade in the ‘drive’ mode.

If there’s a significant degree of clipping after the tone stack, the bass control becomes more of a fart control, and the high gain scooped mid sound requires a further tone shaping section after that clipper, eg the graphic eq of many Boogies.

[Reeltarded]

The guy I bought it from bought it from Gerald off the floor of the Dallas guitar show in '91

There is a 100% chance this is the amp that almost got Gerald killed. This is the amp I joke about constantly. The amp that killed tweed. This very amp. The one you own.

It's infamous.

If you play the intro to Little Sister on it three times in a mirror you summon the angry sprits of Dallas. Promise me you will never do this.

Post TS gain stage is a Lee Jackson idea. There is no normal Marshall design with a post CF/TS gain stage. The fun place to put it is previous to the stage the CF sucks off off. Give it a control and use it as a rally point for all previous stages deciding how hard to hit the PI.

[smokebreak2]

Yea I thought about just moving the switchable stage to before the CF, basically making an 800, or hot rodded marsha thing (and I Still might), but figured if I could get something cooking with this setup, it'd save me some time.

[LOUDthud]

PS I'm pretty sure the OT sec is 4ohm, I can't remember how, I mustve put a meter on the speakers before I boxed them...

I don't think Gerald would have changed the speakers and the OT. He'd be to afraid he'd lose the mojo.

[Reeltarded]

[LOUDthud]

There was a Kendrick amp that was on consignment at Charley's in Dallas for a long time. Head with two cabinets, one cabinet had a 15 inch JBL, not sure about the other. I never got a chance to examine the amp closely, but you have to believe the amp had something other than the 5F6A 2Ohm OT. So it is possible there are amps out there with non-stock OTs. I know the stock 10 inch black frame speakers are 8 Ohms and I've never seen a 16 Ohm version. I've got four of the 8 Ohmers.

[smokebreak2]

https://www.kendrick-amplifiers.com/mm5 ... _Code=0602

There's a link for the 2210 (my model) OT.

Last night I upped that 270K at the grid in #2 to 1M, and that stage has unity gain, and sounds almost exactly the same when I flip the switch, with master dimed.
So at least now I have a MV in the normal spot. In an effort to make to amp sound better, I replaced the 1M bright volume with 250K and a 47p bright cap, and also changed that channels 270K mixer to 470k. Also changed it's coupler to 1500p, and put a 1u over the 2nd stage 820r Rk. Also 12ax7 in V1. Now that channel sounds awesome. I can get the volume up and get some life out of it, the bass is tight and I can run it at 5.