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Build a Sunn Model T clone. Some questions. (EU)
Build a Sunn Model T clone. Some questions. (EU)
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Old 1st February 2015, 10:05 AM   #11
served is offline served
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Join Date: Aug 2011
Got some numbers from the forums.

So it looks like from Hammond, I could use
PT: http://www.hammondmfg.com/pdf/EDB290FEX.pdf
OT: http://www.hammondmfg.com/pdf/EDB1650TA.pdf

But the OT can only handle 120W from the spec and PT is a bit low on HV voltages?
Also the heater current looks low (5.5A).
6550 says it heats 1.6A. 4x1.6 is 6.4A + 3x 12AXT 900mA = 7.3A.
So its not the best, as its low on everyhting. But its cheap.
But I will probably skip this path.

Last edited by served; 1st February 2015 at 10:11 AM.
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Old 5th February 2015, 10:20 PM   #12
okcrum is offline okcrum  United States
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You'd need a Hammond 378 power transformer to approach 200W out. For MI use the 1650T is rated to 140-180 watts.
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Old 18th March 2015, 11:45 AM   #13
served is offline served
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Hi.

I ended up with Mercury Magnetics.
Great service! Huge irons!
Now starting with the chasis drawings and metalworks.
If anyone wants a chasis for MM irons and generation One, let me know!

Lazer can cut more than one.

Last edited by served; 18th March 2015 at 11:54 AM.
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Old 19th March 2015, 02:44 PM   #14
Struth is offline Struth  Canada
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Location: books at londonpower.com
Hi Guys

The Hammond 1650TA OT is rated at full audio bandwidth as 120W. For a guitar or bass you can use it as a 200W part.

The matching PT is the 278CX (378CX for 240V).

This pair of transformers will produce 160Wrms with any set of large-bottle tubes wired as tetrode/pentode. For UL, you can use KT-88 or 6550 PROVIDED the screen-stops are at the recommended value of 1k-5W per tube. Screen-stops should always be correct values and should always be intact for all operating modes.

TUT3 shows this output stage as the Custom Special built by Traynor.

It is important to realise that the range of operation for most of the common tubes widely overlap as does the range of useful primary impedances, so the notion that "you should have Zaa for tube-A" is bunk.

MM is generally a waste of money.

Have fun
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Old 19th March 2015, 03:06 PM   #15
served is offline served
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Good information!
Thanks!
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Old 30th March 2015, 06:21 AM   #16
cyclecamper is offline cyclecamper  United States
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Actually the Fender puts out a lot of power and is a great bass amp.
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Old 30th March 2015, 03:33 PM   #17
Struth is offline Struth  Canada
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Hi Guys

"The reason Marshall have the sound they have is due to the bias setting."

That statement is incorrect, but... it is entirely true if you change Marshall to Mesa. Bias an amp real cold and you have the glorious Mesa sound: lifeless, no sustain, but able to use the cheapest tubes.

Marshalls sound how they do because of poor wiring and grounding schemes - tonnes of intermodulation distortion to make even a clean tone kind of edgey. Dump the CF for a warmer tone and to to have tone controls that DO something.

Fender has the iconic clean sound for both guitar and bass. Their wiring methods were not great either, but they used better OTs than Marshall (who began using surplus OTs/PTs just to get going),m and the 6L6GCs have a more neutral sound. Fender generally did things quite well, since Leo had service experience and access to good quality parts.

The Major is not to be compared with other Marshalls as its circuit is quite different. The PA feedback loop wraps around the EQ and there is only one stage outside this loop. Where the CF in a standard preamp already impedes what the EQ might do, this enclosed EQ has even less effect - the hope was to have more effect. I built a "baby Major" in the '80s and heard it for myself. My curiosity about the circuit was satisfied although the result was opposite to what I expected.

When you build your amp, put the preamp on its own card so it can be easily changed.

Also be sure to include individual bias pots and meter jacks for the output tubes so you can use any tube type and mix them, too.

Have fun
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Old 31st March 2015, 07:24 PM   #18
colorcat is offline colorcat  United States
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Default No Cathode Follower?

So are you saying- "remove the cathode follower and go from there"? Would the builder need to add another gain stage to drive the tone stack or is the existing gain stage sufficient to drive the tone stack after the CF is removed?

I ask as I just built an JTM-45 and it uses the CF so I wonder if removing that stage would enhance tone of the amp?

colorcat.
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Old 31st March 2015, 10:16 PM   #19
Struth is offline Struth  Canada
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Hi Guys

Yes, just bypass the cathode follower. The preceding stage will drive the EQ. TUT6 explains in detail why the CF is there and why it is such a tone killer in the places it is used. The only good place to use one is to drive a line out, or to buffer a pentode plate for maximum gain from the pentode.

Have fun
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Old 1st April 2015, 05:41 AM   #20
colorcat is offline colorcat  United States
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Well I'll have to try that and see since it should require moving only a couple wires. I'll have to go back and check that out on the sch..

Thanks,

Ccat.
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