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| |-+  JTM 45, 50
| | |-+  connecting OT primary to V4 and V5		 « previous next »
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Author Topic: connecting OT primary to V4 and V5  (Read 4392 times)
francois
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« on: December 18, 2012, 10:33:34 PM »
Hi there,

I built my JTM45 kit but with trannies locally purchased in Europe. The OT is an Hammond 1750Q. Regarding color of wires it seems to be exactly the same as the original Marshall diagramm for primary : Red and White + Black for the common.

Now i have to connect red and white to pin 3 of the V4 and V5. I don't know which one is V4 and which one is V5 ( i guess that is the one closer to PT and V4 the one closer to preamps.

I read on another forum it was important to connect in the good way :
Quote
Red goes to pin 3 V4 while white goes to pin 3 V5. If when you power the amp on it turns into the screaming banshee of death, reverse the wires going to pin 5 of each power valve.
So, how to connect?  I would prefer to have the amp working at the 1st  power on  Wink
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T Wilcox
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« Reply #1 on: December 19, 2012, 01:27:04 AM »
Hey francois

On most of the trannies I've used ( Classic Tone usually ) the OT primaries are red and blue and the CT is white.
Hammond may use different colors but you confirm this on your spec sheet.

1st On most all tube amps V1 is the smaller pre-amp tube furthest from the larger output tubes. From V1 the next tube is V2 and the next is V3 and so on....
On the JTM 45 you got
V1 - 12ax7
V2 - 12ax7
V3 - 12ax7  Phase Inverter
V4 - KT66
V5 - KT66
V6 - GZ34 rectifier
Hope that makes sense..

Anyways, Once you figure out which 2 wires are you OT primaries they will land at both V4 and V5 pin 3. You have a 50% chance of having them reversed ( so leave enough wire length). If they are reversed you will know immediately when you power the amp up, it will be the loudest most annoying squealing sound you have ever heard! No worries just desolder and swap the 2 wires and as long as every thing else is wired correctly your amp will be working.

Hope this answered your question

Todd
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francois
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« Reply #2 on: December 19, 2012, 11:29:41 AM »
Hi !

Thank you very much for the precise answer !
Yes, i confirm the color on spec sheet from Hammond

Quote
You have a 50% chance of having them reversed ( so leave enough wire length). If they are reversed you will know immediately when you power the amp up, it will be the loudest most annoying squealing sound you have ever heard
!

OK. I have already anticipated the wire length to reverse in case of . But, with my level in guitar playing , i am 100% sure to produce the most annoying squealing sound ever heard !  Grin
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