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Old 10th April 2007, 11:02 AM   #1
glower is offline glower  Singapore
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Default help needed for 1st DIY tube amp - Sakuma 845 SE

I am not an electronic guy but have done some amp kits. I can understand simple schematics but know nuts about calculating values and designing circuitry.

I am now planning to build my 1st DIY tube amp based on Sakuma's 845 single-ended schematic.
http://www10.big.or.jp/~dh/work/93071.html

Firstly, I would like to add a voltage regulator tube to bias the output tube.

Second, I would like to use a EM80 magic-eye tube as a VU meter.

Can anybody help me with the schematic?

Thanks a million!

- Louis
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Old 10th April 2007, 04:41 PM   #2
kevinkr is offline kevinkr  United States
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Fixed bias with regulation is not a good idea in a triode amplifier with unregulated plate supply. Plate current will vary significantly as a function of varying plate supply voltage. Cathode bias as implemented here will result in relatively consistent performance over some range of line voltage and tube variation.

I'd build as designed otherwise you are building something else.
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Old 10th April 2007, 08:09 PM   #3
gianis is offline gianis  Greece
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Default se

I propose ...dont try this schematics..maybe something else more simple...
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Old 10th April 2007, 08:22 PM   #4
glower is offline glower  Singapore
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Thanks Kevin, I've got what you mean. I will stick to the original schematic.

What about the VU meter with EM80? Any help?
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Old 10th April 2007, 08:32 PM   #5
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I'm with gianis, DON'T build an 845 amp as your 1st project. The risk of death from electric shock is all too real.

IMO, you should pick something that operates at a lower voltage. When, not if, you make a mistake, your chances of surviving, with only a damaged ego, are better.
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Old 10th April 2007, 08:36 PM   #6
phn is offline phn  Sweden
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I will never say "search this forum" because for all I know, the search doesn't work.

But if you look for schematics, please start with google, image search in particular.

Maybe this? http://koti.mbnet.fi/siliconf/JukkaT...r/peakmtr.html

Edit: I second the concerns expressed here.
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Old 10th April 2007, 08:37 PM   #7
agent.5 is offline agent.5  United States
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Quote:
Originally posted by Eli Duttman
[B]I'm with gianis, DON'T build an 845 amp as your 1st project. The risk of death from electric shock is all too real.

But potential death is related to high B+ and not usage of 845. The schematic, in question, uses 500V B+. So, you are probably in as much danger as building a 6550 amp or a 300B amp.

I think OP will be fine. Make sure you wear electric gloves and read and read the thread about safety and high voltage.
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Old 10th April 2007, 09:31 PM   #8
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100 ohm volume pot?

That's one heckuva preamp driving this thing.
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Old 10th April 2007, 09:47 PM   #9
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Quote:
Originally posted by Eli Duttman
I'm with gianis, DON'T build an 845 amp as your 1st project. The risk of death from electric shock is all too real.

IMO, you should pick something that operates at a lower voltage. When, not if, you make a mistake, your chances of surviving, with only a damaged ego, are better.
Yes, the voltages are high for a first project, but my sense is that the build complexity is also too high. Looks like a very expensive hum generator to me.
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Old 10th April 2007, 09:48 PM   #10
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Quote:
Originally posted by zigzagflux
100 ohm volume pot?

That's one heckuva preamp driving this thing.

Could just be a cd player with an opamp on the output. Zout is pretty close to 0.
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