Half a Major Build

Marshall Amp Discussion

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fusionbear
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Half a Major Build

Post by fusionbear »

Someone commissioned this from me and I forgot to post it. It also had a switchable 1 wire cascade mod. I used the Classictone/Dynaco Clone PT and OT to give about 565+ on the plates of the two KT88's.

[img:3264:2448]http://i.imgur.com/9nzahbK.jpg[/img]

[img:3264:2448]http://i.imgur.com/Gup41iS.jpg[/img]

[img:3264:2448]http://i.imgur.com/NtFcSik.jpg[/img]

[img:2448:3264]http://i.imgur.com/om4fheo.jpg[/img]

[img:3264:2448]http://i.imgur.com/NjlvtTm.jpg[/img]

[img:2448:3264]http://i.imgur.com/Z6IegfI.jpg[/img]

And a clip:

https://www.youtube.com/watch?v=aBADx0TlrCI
Bombacaototal
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Re: Half a Major Build

Post by Bombacaototal »

Nice!! Thanks for sharing

How does it compare to the 200watt original monster sound wise
v846
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Location: T-Ville, CT

Re: Half a Major Build

Post by v846 »

Nice neat wiring, I like how you did the heaters :). Sounds great

db
fusionbear
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Re: Half a Major Build

Post by fusionbear »

Bombacaototal wrote:Nice!! Thanks for sharing

How does it compare to the 200watt original monster sound wise
It has the tone without the bone crushing loudness. But if I were building one for myself, I would do the 4 KT88 version but with the lower 560 or so B+ just to get the full effect....
Learning to learn...
fusionbear
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Re: Half a Major Build

Post by fusionbear »

v846 wrote:Nice neat wiring, I like how you did the heaters :). Sounds great

db
Merlin Blencowe style. I do that with all my amps now...
Learning to learn...
Bombacaototal
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Re: Half a Major Build

Post by Bombacaototal »

fusionbear wrote:
Bombacaototal wrote:Nice!! Thanks for sharing

How does it compare to the 200watt original monster sound wise
It has the tone without the bone crushing loudness. But if I were building one for myself, I would do the 4 KT88 version but with the lower 560 or so B+ just to get the full effect....
That's a good idea. How many watts would that be? I think one would even be able to fit the circuit on a smaller size head for better transportability

Do you have the schematic/ layout you used by any chance
Bob S
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Re: Half a Major Build

Post by Bob S »

Another nice one Bear. Well done.
Someone is getting a great gigging rig - it looks very robust.
I don't know why, but I avoid building anything with a B+ higher than 500v.
Maybe soon. Hmmm.
Why Aye Man
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martin manning
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Re: Half a Major Build

Post by martin manning »

Very neat, and good idea to use the Dynaclone transformer set. BTW, which model Classic Tone transformers did you use? A-431S OT and P-782S PT?

If it's a half-Major, I guess you have to call it a Warrant Officer?
v846
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Re: Half a Major Build

Post by v846 »

fusionbear wrote:
v846 wrote:Nice neat wiring, I like how you did the heaters :). Sounds great

db
Merlin Blencowe style. I do that with all my amps now...
Interesting, have you noticed a reduction in heater hum compared to the loop around the socket wiring used in old Marshalls?

Thanks,
David
fusionbear
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Re: Half a Major Build

Post by fusionbear »

martin manning wrote:Very neat, and good idea to use the Dynaclone transformer set. BTW, which model Classic Tone transformers did you use? A-431S OT and P-782S PT?

If it's a half-Major, I guess you have to call it a Warrant Officer?
Yep... that set.
Learning to learn...
fusionbear
Posts: 478
Joined: Thu Nov 01, 2007 4:42 am
Location: Southern California

Re: Half a Major Build

Post by fusionbear »

v846 wrote:
fusionbear wrote:
v846 wrote:Nice neat wiring, I like how you did the heaters :). Sounds great

db
Merlin Blencowe style. I do that with all my amps now...
Interesting, have you noticed a reduction in heater hum compared to the loop around the socket wiring used in old Marshalls?

Thanks,
David
It is very slight, but my amps are quiet anyway due to using good grounding points to begin with.
Learning to learn...
fusionbear
Posts: 478
Joined: Thu Nov 01, 2007 4:42 am
Location: Southern California

Re: Half a Major Build

Post by fusionbear »

Bombacaototal wrote:
fusionbear wrote:
Bombacaototal wrote:Nice!! Thanks for sharing

How does it compare to the 200watt original monster sound wise
It has the tone without the bone crushing loudness. But if I were building one for myself, I would do the 4 KT88 version but with the lower 560 or so B+ just to get the full effect....
That's a good idea. How many watts would that be? I think one would even be able to fit the circuit on a smaller size head for better transportability

Do you have the schematic/ layout you used by any chance
It is about 90 watts. As for a schematic, I didn't draw one. I used the original PA version of the Major as a starting point. I also lowered the first stage filter caps to 250uf each in series since this is only for two KT88's. The PT requires half wave rectification like a 50 watt type Marshall PT, so I had to adjust the circuit there.I used a 500pf bright cap on the Bright channel and used a 500pf across the mixer. The tone stack is Bass spec with the exception of a 47k slope resistor. I experimented with layouts on the turret board until I discovered what would work best. You can see some changes in the pictures I posted. Also, it is using the so called "Rich mod" PPIMV dual 500k PEC pot. I like this PPIMV on this amp because it lets you bring up the volume more slowly. Also, because it kills the negative feedback at lower settings, it lets you get that looser VH1 feel with the cascade mod on. In order to do the cascade mod properly, I used a .0022 coupling cap on the normal channel. You plug into that channel if you want to cascade. I also used a 100uf cathode bypass cap on the shared cathodes of V1. I played around with several values as low as 10uf to as high as 330uf but, the 100uf seemed to give the best overall results.
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