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PostPosted: 21 May 2010, 22:32 
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I was just looking at another thread by a noob who is using Corian (a counter top material) for his amp cabinet.

I don't know about anybody else but drilling large holes in steel is a nightmare unless you have expensive tools for the job. This Corian looks like it's much easier to work with.

Assuming I want to use a steel chassis but use a top made of a different material to facilitate construction, what's a good material?

I'm considering a thick sheet of Lexan or possibly Corian now. What else is there? A thick piece of aluminum might not be bad, but it would have to be very thick to keep from bending, making it hard to cut. A copper sheet would work as well, but again, it has to be heavy enough not to bend easily.

Lexan is my top choice so far unless anybody has a suggestion, or possibly Lexan with a thin sheet of metal laminated together with the metal on the inside. It needs to hold together and not permanently bend or break under the weight of 3 large transformers attached to it. This is obviously for the GM70 project.

The only thing about Lexan is that it won't hide my ingenious, patented, proprietary, computer modeled, 3D optimized wiring methods.

Thanks.

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PostPosted: 22 May 2010, 02:52 
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With the B+ at 1200 volts and the bias at 100 mA, the 6E5P in an SRPP configuration will only push the GM70 tubes to 56% of their power capability, so it's time to find a new driver tube.

Looking for driver tube suggestions again. Are there any Russian dual triodes out there that would do the job in a SRPP circuit? I want something that will do the job with ease, not something I have to push to its limits. The GM70s should be the only tubes getting pushed hard.

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PostPosted: 22 May 2010, 03:20 
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What about use ETALBOND ? double aluminum sandwich - 5 mm
http://www.iris1989.com/etalbond.html /sorry, I founded only in bulg. lang., there is some pictures/
http://picasaweb.google.bg/azazello52/A ... 0421321074

I think 6E5P in penthod mode has some hundred mu and will drive your tubes. But You can try...

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Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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PostPosted: 22 May 2010, 04:20 
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azazello wrote:
What about use ETALBOND ? double aluminum sandwich - 5 mm
http://www.iris1989.com/etalbond.html /sorry, I founded only in bulg. lang., there is some pictures/
http://picasaweb.google.bg/azazello52/A ... 0421321074

I think 6E5P in penthod mode has some hundred mu and will drive your tubes. But You can try...

How can a tube with a maximum anode votage of 250 volts provide the 240 volt peak to peak output needed to drive the GM70? The mu could be a million. If the tube can't handle the voltage what good is it?

A 6SN7 with a B+ of up to 450 volts looks like a good choice, but I'd prefer a cheaper Russian tube if I can find one. I want a triode, and I want to use two in a SRPP stage. That's the design. Now I need the appropriate tube. It can be a pentode run as a triode - that's fine.

i'll check ebay for Russian dual triodes and see what's available if anything.

Maybe I'm missing something, but I just don't see how the 6E5P could swing 240 volts on the output in pentode or any other mode.

I have one other concern, and that is the AC voltage on the cathodes and the current source. If it exceeds about 55 volts the LM324HV won't work. I can compensate for the DC offset but there will still be an AC swing on the output of the CCS, and the highest voltage the LM317HV can handle is 55 volts. I need a PSPICE model to calculate the swing on the cathodes - I'm not smart enough. I'll try a similar American high voltage power triode model and see what the results are.

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Last edited by sampleaccurate on 22 May 2010, 04:34, edited 1 time in total.

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PostPosted: 22 May 2010, 04:29 
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Here's how the GM70 and 6E5P are hooked up for an SE config in my Russian book of tubes.

Image

GM70 has a mu of 6,7.

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PostPosted: 22 May 2010, 04:41 
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Soundbrigade wrote:
Here's how the GM70 and 6E5P are hooked up for an SE config in my Russian book of tubes.

Image

GM70 has a mu of 6,7.

What's the voltage at the top of the resistor connected to the plate of the 6E5P?

What's the AC voltage swing at the output of the pentode driver stage?

The grid of the GM70 needs 240 volts peak to peak drive to achieve full power. Check out the load line.

The specs say the plate voltage can't exceed 250 volts for the 6E5P (to the best of my ability to read them). That being the case, how can it possibly work? Am I reading the specs wrong? What am I missing?

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PostPosted: 22 May 2010, 05:11 
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Do you think a 6H8C (6SN7 equivalent) in an SRPP stage would work? It appears to me it would with a B+ around 350 volts. The max B+ for this tube depends on the datasheet or book referenced.

http://tubedata.milbert.com/sheets/113/6/6N8S.pdf

I may need to use a 6SN7 that's capable of a higher B+.

It's not just the gain and power output. I'm not using interstage transformers here. I need the driver power in the form of the correct voltage and output impedance. All the gain in the world or even all the power output in the world won't do any good if it's at low voltage and high current. I need high voltage / low current, and without a B+ significantly higher than the 240 volts of output swing needed to drive the GM70 I don't see achieving that goal.

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PostPosted: 22 May 2010, 05:44 
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You are in deep problems my friend ... ;) I have the "same" problems, but I have quite another a tube (EL156), that doesn't need that much to start rocking. :smoking: .

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PostPosted: 22 May 2010, 06:23 
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Soundbrigade wrote:
You are in deep problems my friend ... ;) I have the "same" problems, but I have quite another a tube (EL156), that doesn't need that much to start rocking. :smoking: .

How about this? A SRPP stage using a 6SN7 with an output swing of over 260 volts. It can handle much higher voltages than the 6E5P.

Image

Image

I put a 10K resistor in series with a 10uf cap to load the amp to simulate what seems to me a lot lower impedance than the GM70 will present. The tube is dissipating about 4.2 watts between the two triodes, or a little more than half its total rating.

Any thoughts? I will need some gain before this stage, but not much, to make it compatible with low level sources.

It looks like a winner to me.

I could try a 6N8S at 400 volts B+ and see what happens. The curves in the book show 380 volts but the specs seem to say max plate voltage is 250. Maybe that's the operating voltage. But it sure looked to me like the "equivalent" 6N8S to the 6SN7 couldn't handle the same voltages.

Could you look at the specs in the Russian book Magnus and tell me how high of a voltage I can run a 6N8S (6H8C in Russian)? It's so much less expensive than the 6SN7.

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PostPosted: 22 May 2010, 07:00 
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Output signal from 6E5P must be = -U bias. in Your case -100 - -120v !
Please, see Magnus schematic ....+U anode-cathode 6E5P is 140 +_ 5V !!! And Ubias is maybe -100- -120 v !!
Maybe, sorry, something You are wrong.....The schematic is right! Please, think again!
I think that 6E5P is right tube to drive GM70 in 2 stages ampl.!

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Hi End is back proportional to the number of composite parts!
Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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