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Old 26th February 2013, 12:18 AM   #51
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Originally Posted by mr2racer View Post
Hello Again All,

Can anyone tell me what wattage the 100ohm pot in the CCS needs to be? And is it just connected on the one end and the wiper? And does all the DC current go to ground through the lower tubes grid?

Kevin
I used a small bourns trimpot.....just connected at one end and the wiper.
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Old 3rd June 2013, 02:58 AM   #52
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Hey All,

I'm finally getting started on my music machine(s). I'm going to use Eico ST70 iron with a second power transformer.

I plan to have Heyboer build me another power transformer so I can build a pair of 6550C MM monoblocks. They'll have 438 volts of B+ at 94ma per 6550. With 188ma for the outputs and 24ma for the CCS 6GK5's, at 212ma the power transformer will have some nice headroom. The amp should produce a little over 30 watts. With the Z out of 4k the 16 ohm becomes 8 and the 8 ohm becomes 4.

Is there anything I can do to get a little more drive out of the 6gk5's? More current? Higher B+?

Kevin
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Old 3rd June 2013, 03:44 AM   #53
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Is there anything I can do to get a little more drive out of the 6gk5's? More current? Higher B+?

Kevin
Mosfet followers......look at Sgregory's Opus project or Chrish's 6L6GC AB2 project. You can probably drop the entire mosfet stage from either of these right into the MM.

OPUS 5.0 A Modern Mullard

6L6GC AB2 Amp
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Old 6th June 2013, 01:13 AM   #54
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Boywonder,

Read the thread for the Opus, couldn't find the 6L6GC amp. The power supply and the mosfets seem a little more complicated than I'm ready to get into just yet. Is there any reason I couldn't use a tube cathode follower? Would 6CG7 be a good candidate?

Kevin
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Old 6th June 2013, 02:31 PM   #55
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Originally Posted by mr2racer View Post
Boywonder,

Read the thread for the Opus, couldn't find the 6L6GC amp. The power supply and the mosfets seem a little more complicated than I'm ready to get into just yet. Is there any reason I couldn't use a tube cathode follower? Would 6CG7 be a good candidate?

Kevin
I imagine that you could use a tube cathode follower......mosfet followers are pretty straightforward, you just need an additional power supply. I'm no expert here, but I believe the negative rail needs to exceed the -ve bias voltage with a little headroom, and the +ve rail allows some A2 operation. I think you need a little +ve voltage for the mosfet drain to provide some headroom even for AB1 operation.

Late in the 6L6GC AB2 thread there is discussion about KT88 operation.

Are you planning on using a preamp? You still have limited voltage swing of the 6GK5 to deal with when driving 6550/KT88. Since an LTP gives you 1/2 mu, you can only swing about +/- 39V or so with the 6GK5. To fully drive 6550's/KT88's you need around +/-50V or so.

Using a higher mu LTP will give more voltage swing and using a cathode follower or a mosfet follower will provide the current needed, although the amp will no longer be a MM.
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Old 6th June 2013, 11:47 PM   #56
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Thanks Boywonder,

I've decided to build a straight EL34 MM using EL34's. I'll save the 6550's and the Eico iron to build a pair of Dynaco Mark III's in triode after I finish the MM. Thanks very nuch.

Kevin
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Old 7th June 2013, 12:58 AM   #57
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Hey,

I got an email from John Broskie and something he said as well your posts got me thinking. Am I correct in thinking that to drive a tube to full output you have to swing plus or minus the bias voltage on the grid?
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Old 7th June 2013, 01:47 PM   #58
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Originally Posted by mr2racer View Post
Hey,

I got an email from John Broskie and something he said as well your posts got me thinking. Am I correct in thinking that to drive a tube to full output you have to swing plus or minus the bias voltage on the grid?
Yes. For AB1 operation, you need to swing +/- the grid bias voltage. For AB2, you need a little more, so that the grid voltage can go positive.

Folks usually want the small signal tubes to drive more volts and current than the outputs require for some robustness. Keep in mind that if your input/LTP stage can swing more voltage than the outputs require, the small tube's output will be more linear, ie less distortion.
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Old 8th June 2013, 03:36 AM   #59
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Default Sovtek 6B4G

Eli Duttman
The 6BGs from the Siberian Shop rate to be Soviet NOS and lack the toughness of current production Sovtek 6B4Gs. AFAIK, New Sensor uses the same anode stamping for 6B4Gs and 300Bs, for economy of scale. It's no wonder that their 6B4Gs are tough. __________________
Eli D.
I see from the Sovtek data on the 6B4g and 2A3 Sovtek claims only 15 watts.
Compared to the Single plate RCA 2A3 also 15 watts: i have the Sovtek plates are much larger. I notice the Shuguang also only cliam 15 watts for their large 2A3's
Why?
Thanks
Phil
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File Type: pdf 6b4g-sovtek.pdf (285.8 KB, 15 views)
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Old 27th June 2013, 09:51 PM   #60
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Hey Anyone,

I just noticed the diode in the MM schematic after the 332 ohm resistor connecting to grids 2 and 3. It doesn't look like a zener symbol so is it just a regular diode? Any particular value or type? And can anyone tell me its purpose?

Kevin

Kevin
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