• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

help needed for 1st DIY tube amp - Sakuma 845 SE

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G

glower

Member
Joined 2007
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
 
kevinkr

kevinkr

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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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Eli Duttman

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Joined 2004
I'm with gianis, DON'T build an 845 amp as your 1st project. :att'n: The risk of death from electric shock is all too real. :hot:

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.
 
A

agent.5

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Joined 2003
Eli Duttman said:
I'm with gianis, DON'T build an 845 amp as your 1st project. :att'n: The risk of death from electric shock is all too real. :hot:
Click to expand...



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.
 
dsavitsk

dsavitsk

diyAudio Member
Joined 2005
diyaudio.ecp.cc
Eli Duttman said:
I'm with gianis, DON'T build an 845 amp as your 1st project. :att'n: The risk of death from electric shock is all too real. :hot:

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.
Click to expand...

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.
 
kevinkr

kevinkr

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I thought about warning against building this design, but didn't because unlike many typical 845 designs the voltages here are in the same range as you would see for a drd/monkey/freelunch direct coupled design using a 2A3 or 300B.

500V is not a particularly low voltage, but the original poster indicated he did have some experience building amplifier kits. Obviously he should carefully read and understand the safety and high voltage threads.

The design is not overly complicated and can be driven by any transformer coupled pre-amplifier, and as Doug pointed out, any number of cd players. (portable anyway)

I knew someone a few years ago who built one of these successfully from scratch and had little experience prior to doing so. The amplifier even sounded good.

Good construction practices are a must, and obviously looking at the original Sakuma drawings. pictures. and schematics should help in this regard, as will asking lots of questions here.

Louis, in answer to your question I don't have any good circuits for a VU meter with the EM80. There was an article some years back I think in AudioExpress's predecessor Glass Audio about using tuning indicator tubes for this.. Try googling you might find something.
 
A

Audio_idiot

Member
Joined 2006
glower said:
Thanks guys for all the concerns. Like I mentioned in my 1st post, I have done some amp kits. That includes SS 100W FET amp, SS preamp, and a EL84 SE. This is my 1st DIY amp which is not a kit.

So, anyone can help me with the EM80 schematic?
Click to expand...


Hi,

500V B+ isn't particularly dangerous (even though it will kill the same as 200V B+ or even 80V...) but cost a FEW arms and a FEW legs on 845 and Tamura irons... Also, it's going to be huge and heavy..

For a 1st amp, it's a good bet to rebuild your EL84 SE from scratch. Trace the circuit and build point-to-point. New resistors and capaciors, and maybe new sockets is all you need. this will put you up to speed. Moreover, this will take out the frustration of decisions on the irons... AND chassis.... another bonus is that you will know how the result would be...

Then, you can put in your VU meter, cat eye, regulator, spectrum, LED, LCD,.... which ever suits you...

BTW, IMHO, voltage regulation isn't that neccesary in an power amp... but if you just want an excuse to practice soldering, then by all means...

Just my 2 cents
 
G

glower

Member
Joined 2007
I have just came out with a simple schematic for the EM80 but I have no idea will it work or if it is correct. Any comments will be appreciated!
An externally hosted image should be here but it was not working when we last tested it.


B = ~550-600VDC

Can someone help me with all the values if the schematic is correct?
Below is the datasheet of the EM80.
http://frank.pocnet.net/sheets/030/e/EM80.pdf

I wonder where should "X" be connected to...
Can it be connected between the interstage trans and the output tube?
Below is the main schematic.
http://www10.big.or.jp/~dh/work/93071.html
 
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