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Old 12th October 2010, 03:14 PM   #1
jonas86 is offline jonas86  Italy
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Default Bassman 100 schematic questions

Hallo!

I would like to build a tube amplifier and i will be my fisrt time, i have choose a Bassman 100 but i'm not able to understand same things:

- Someone has a datasheet or know the voltages of the transformator because i think that i can save money if let them make directly from a company, i have found somthing :

350 - 0 - 350 V, 350 mA
6,3 V, 4A for the 6l6 and 2A for the 12AT7 and 7025

And the voltage for the bias?
And TR2? What is his role?

- In the schematic (black "circle"), if i'm right there is a balance pot 10k, but a potentiometr has 3 terminals and there are 4 wires, so how must it be connect?

Thanks a lot,
Jonas
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Old 12th October 2010, 03:46 PM   #2
Gilgy is offline Gilgy  United Kingdom
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TR2 is a power supply smoothing choke, the bias supply is taken from a tap on TR1 via half-wave rectification. The extra terminal on the bias trim pot is a fixed tap on the pot's carbon track - these pots can be very difficult to source and the schematic doesn't mention what resistance the tap is at. I'd look at redesigning that section unless you can find a schematic showing the correct valuefor that pot.
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Old 12th October 2010, 03:56 PM   #3
Merlinb is online now Merlinb  United Kingdom
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Quote:
Originally Posted by jonas86 View Post
Hallo!
In the schematic (black "circle"), if i'm right there is a balance pot 10k, but a potentiometr has 3 terminals and there are 4 wires, so how must it be connect?
It is a 'tapped' potentiometer. (It has a centre connection, so it has four terminals).
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Old 12th October 2010, 04:00 PM   #4
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Try Antique Electronic Supply for the transformer. They sell transformers that are specifically intended for use with the popular amplifier designs.
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Old 12th October 2010, 07:31 PM   #5
jonas86 is offline jonas86  Italy
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Thank you very much!
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Old 12th October 2010, 09:27 PM   #6
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by jonas86 View Post
Hallo!

I would like to build a tube amplifier and i will be my fisrt time, i have choose a Bassman 100 but i'm not able to understand same things:
...
This is NOT the best first project. It is far to complex if you have never build a tube amp before. Yes it seems all you do is follow the schematic but, no construction details really matter.

I'd suggest a Fender "Champ". It's a single ended 6V6 based amp that is much more simple.

Also do you really need 100W? Most people don't. Would be interested to hear how you determined the amount of power you need.
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Old 13th October 2010, 10:43 AM   #7
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Why not go with the 50w bassman. A better sounding amp in my opinion. That pot you have marked on the schematic is the rather silly bias pot that did not actually set the bias as a whole but actually "shared " the voltage between the 2 or 4 output tubes they called it output tube matching and is on all silverface models. This is easily moded out to blackface specs. Try and find a schematic for an earlier bassman. It will be cheaper to build sound better and will not have that funny bias arrangement.
Mario.
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Old 13th October 2010, 12:12 PM   #8
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jonas86 - Its true that the pot on the 100W bassman is a pretty silly way to do things, but surely not the only way to achieve the same result. I understand why you would want the extra power but if you would like to spend some time poking around at other classic designs take a look at "schematic heaven" which can be found at Schematic Heaven. Where all good Amp designs await resurrection...
They have reciently undergon some problems with the site, but boy what a good resource for folks intrested in the classics.
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Old 15th October 2010, 09:43 PM   #9
jonas86 is offline jonas86  Italy
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Well i don't know if i really need 100w, and probably not... But i was very excited with the idea to build something powerfull!
I already bought the tubes.... So now i'm focused on this one...

But ok, as you suggested i will take a look to the champ and to the bassman 50w.

In any case could you help me to change the bias arrangement? I have read somewhere that i could repalce the 15k resistor and the 10k pot or trimmer with a 25k trimmer is that correct?

Thanks for your opinion!
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Old 15th October 2010, 10:00 PM   #10
jonas86 is offline jonas86  Italy
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And what do you think abaut an Ampeg b 15?
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