bassman 100 &nb

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chrisefekt
Junior tube assistant
Posts: 1
(3/3/04 10:48 am)
  bassman 100
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 Hello all...I'm new here so please excuse any dumb questions I might or will ask. Have a mid 70's bassman 100 amp. Would like to modify this thing for more gain, tone, maybe covert to EL34's, and at the same time learn about tube amps in general. Any advice or suggestions on my quest for tone and knowledge is greatly appreciated. Any books or videos that anyone could suggest would be cool as well. Thanks

Chris

EDIT: I moved this post here. It was posted in the Archive forum.

Ken

Edited by: GroundhogKen at: 3/3/04 11:21 am
 
Tiny Daddy
I will work on all amps
Posts: 523
(3/3/04 10:47 pm)
  Re: bassman 100
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 The Bassman 100 seems to me a well-designed amp. You may want to install some modern diodes in the power supply, double the first filter caps to 220uF if there is room for them, and remove the .047uF cap on the ground lift switch. I would not convert to the lower dissipation, higher filament current EL34's. You may want to add a bias voltage adjust. Of course you should replace all of the old electrolytic capacitors if this has not been done recently.
 
ganzonimx
Hey get your own solder
Posts: 419
(3/4/04 10:25 am)
  Re: bassman 100
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 I agree with Tine Daddy completely. I have a Super Bassman and after servicing it with new filter caps, orange drop's and micas it sounds great.

If you use the Illinois 100uf/350 caps (the one Doug sells) for the first filter stage you will get easily 4 caps under the cap can. You have to just turn them 90 degrees. Of course you have to redesign the filter cap board.

I changed also the 10K mid pot on the bright channel to a 25K, that gives you the option to get a more crunchy sound (is that the right word for more mids?).

You could get more power and a even more clean sound out of it if you switch to a ultra linear OT. The Hammond 1650T should do that job. If I had such a transformer on the hand I would give it a try.

Cris
 
chrisefekt
Posts: 2
(3/4/04 1:48 pm)
  bassman 100
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 Thanks so much for the input guys. This is my first amp project, so i'm not so concerned with screwing up (have many other tube amps, this one is disposable if need be). I think I can handle replacing parts...how do i go about adding a bias voltage adjust? And why not the EL34's. Was looking for a different sound?
Chris
 
Funkalicousgroove
Junior tube assistant
Posts: 10
(3/4/04 4:38 pm)
  more gain
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 If you want to add more gain you can increase the values of the plate/cathode resistors to 220k/3k3, you should also drop the values of the cathode bypass caps to 5uf or so, this will tighten up the low end.
 
Funkalicousgroove
Junior tube assistant
Posts: 11
(3/4/04 4:48 pm)
  EL34
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 The EL34's draw too much curent to use 4, you'll overheat your power tranny, It should handle 2 tubes okay though. remember to tie pins 1 and 8 together
 
ganzonimx
Hey get your own solder
Posts: 421
(3/4/04 5:15 pm)
  Re: more gain
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 I thought that is the way around:

the higher the bypass cap, the better the bass response and the higher the gain of the stage ... but it's the case that the bass channels on the 100 and 135 Bassman has a 5uF bypass cap, the normal channel has a 25uF on the first stage.

FGroove, can you shed some light on that?

Cris
 
Funkalicousgroove
Junior tube assistant
Posts: 13
(3/4/04 6:56 pm)
  bypass caps
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 That sounds right, the smaller the value the less bass response, keep in mind that your bass channel is set up for a bass, so it doesn't need the extra response. Changing to a 5uf will decrease the bass response, but changing your plate/cathode resistors will increase the gain substantialy. The idea here is to add usable gain that doesn't sound "farty" or "roll"; by decreasing the bass and increasing the mid and treble response your amp will take on a new "singing" quality. The first stage of most high gain amps like bogner or boogie is bypassed with a .68uf, they have plenty of bass response for a guitar. How Much modification are you going to do to this amp? if you are going to add high gain distortion you may even want to go smaller values on the bypass cap.
 
ganzonimx
Hey get your own solder
Posts: 424
(3/4/04 7:37 pm)
  Re: bypass caps
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 THX FGroove  

Cris
 
chrisefekt
Posts: 3
(3/5/04 7:00 am)
  bassman 100
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 I'm willing to modify this thing to no end. And yes high gain distortion is what I'm after, but not to sacrifice overall tonal quality!
Chris
 
Funkalicousgroove
Junior tube assistant
Posts: 14
(3/5/04 10:32 am)
  Tone search
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 What type of high gain are you after? Do you want like a Boogie or something smooth? If you're after more of a marshally distortion you should move the tone stack so that you can add more gain stages in front of it, If you want "singy" distortion ala robben ford you should put the extra gain stages after the tone stack. Try blueguitar.org for some schematics.
 
chrisefekt
Posts: 4
(3/5/04 11:17 am)
  gain type
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 Yea...I guess boogie type, but I would like to experiment so i have some options.
Chris
 
Funkalicousgroove
Junior tube assistant
Posts: 15
(3/5/04 6:41 pm)
  suggested reading
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 Here are some books you should read:
1. The Tube Amp Book by aspen pittman
2. Tube amp talk by Gerald Weber
3. Desk reference guide of Hip Vintage guitar amps by Gerald Weber
4. Dave Funk's Tube Amp Workbook
5. Valve Amps by Morgan Jones
6. The audio cyclopedia by Howard tremaine (1969 ed)

Duncanamps.com has a small program you can download called a tone stack calculator, you can plug in different values for components and It will show you how they will affect the frequency response.
 
 
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