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Old 22nd December 2008, 10:18 PM   #21
45 is offline 45  Italy
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Quote:
Originally posted by VictoriaGuy


It's sounds like it is a re-issue amp, so one needn't be too concerned about historic value in that case.
One does need to be careful, though, since most of the reissues are built on pcb and don't always hold up well to a lot of soldering and swapping of components.
Cheers
John
I didn't notice that.
Anyway, as you say, with a lot of soldering and swapping it could loose its actual value as well.


Cheers,
45
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Old 23rd December 2008, 03:57 AM   #22
packman is offline packman  Italy
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Default from 2000

Yes, the amp is from 2000 so is not a point-to-point wire circuit
but have pcb, for now i have only paralleled R6-C6 with a wire
and paralleled C2 with a larger cap so the mods can easily removed
Sure that if i can have the wanted results swapping only one or 2 valves is more simple but for me is a way to learn something about valves and the way they works/sounds (possibly doing a non-destructive interventions!)
Now i'm looking for 2 goods valves to modify the 2 ECC83.
What is the exact function of valve 1 and 2?
Thanks
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Old 23rd December 2008, 04:43 PM   #23
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V1A is the input preamp, V1B is the post volume control gain recovery, V2 is the phase inverter.

I would leave V2 alone as it isn't going to have that much effect on the clean sound you are looking for. V1A is the most important stage here. It is the stage that gets overdriven first by using humbucking pickups. Humbuckers tend to have much higher output than single coils especially when comparing Gibson guitars to Fender guitars.

This is also why the plate resistor on V1A needs to be changed to a 100K. This will drop the gain of the first stage even if the 12AX7 is left in.

Unfortunately, the first two stages are part of the same tube. What you would really like is to change V1A only to a lower gain stage and keep V1B as the 12AX7. Dropping the gain in V1A will cause the volume control to be turned up higher for the same output level. Having V1B also drop in gain forces the volume control to be turned up even higher to achieve the same output level.
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Old 23rd December 2008, 04:58 PM   #24
packman is offline packman  Italy
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Thanks guitar88
The effect that i don't want is a type of "squelch", a saturation effect that made the mids and highs a bit harsh when the volume of the guitar is high.
Have that resistor a minimun value usable to control the gain of V1A?
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Old 24th December 2008, 06:21 AM   #25
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packman,

I can't suggest what tube you may test to change first. YOU MAY DO TESTS!

If you have some tubes, you could do tests. Change a Tube and play music. You can found your sound at this way.

Regards,
Felipe Navarro
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Old 24th December 2008, 08:00 AM   #26
packman is offline packman  Italy
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Hi Felipe, at home have only 12AX7 now (a phono preamp) and some electronic components, if i have the valves sure i would try! i'm informing on where can found them but you know now i have few holidays and shop are closed for Christmas so in th meantime i can try to add some resistors/caps in parallel here in there (like advised) and hear what happen, all reversible operations
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Old 25th December 2008, 07:43 AM   #27
packman is offline packman  Italy
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Default Love this guitar sound

This is the sound i have in mind :

http://www.youtube.com/watch?v=0MmMn273f54

love expecially that warm and clean chords, nice!

Happy Christmas DIYholics and thank for all!
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Old 25th December 2008, 03:41 PM   #28
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Wow.

It's a work for a Jazzy amplifier. To go at this way, you can change the input tube for a 12au7, 12ay7 or 12at7. These tubes is very inexpensive and it is good if you can buy someone to test.

I think you can start changing the firts 12ax7 with 12at7 and if you see a lot of gain. You can do the mod to chance R1 into 100k. If you bypass the capacitors of the power supply with a 100nF capacitor. It will be good too.

Can you go to this sound at this video here?
http://www.youtube.com/watch?v=Jx3hd8jHYhU

I think you can have your song with the 12at7 or 12ay7. Modifications can be good too.

Regards,
Felipe Navarro

Merry Xmas for you too.
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Old 25th December 2008, 05:24 PM   #29
packman is offline packman  Italy
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Thanks Felipe! Have you advises regarding valves brand?
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Old 25th December 2008, 07:38 PM   #30
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packman,

Last month I worked on a Crate VC5212 with JJ Testa 12ax7 ( NEW, don't be confused with NOS ) and I dislike them. If you will buy new production tubes, you can buy Sovtek. I like them.

But... NOS tube are great!

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