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Post subject: Fender excelsior lost power
Posted: Mon Sep 23, 2013 11:46 am
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I have an Excelsior that has lost about half power. Installed new tubes and it did not help. You can remove the 12AX7 from V2 and it makes no difference at all. Also the tremolo has quit working. And ideas?


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Post subject: Re: Fender excelsior lost power
Posted: Mon Sep 23, 2013 12:12 pm
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If you remove V2, you should have no output at all, as half of V2 id the PI which drives the output tubes.

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Post subject: Re: Fender excelsior lost power
Posted: Tue Sep 24, 2013 9:33 am
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if i remove V1 amp quits completely. But, as I said before, With V2 tube in or out make no difference at all. Amp is about half as loud as it should be.


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Post subject: Re: Fender excelsior lost power
Posted: Tue Sep 24, 2013 10:42 am
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Maybe the tremolo switch is failing?


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Post subject: Re: Fender excelsior lost power
Posted: Tue Sep 24, 2013 1:36 pm
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jdawgsmusic wrote:
if i remove V1 amp quits completely. But, as I said before, With V2 tube in or out make no difference at all. Amp is about half as loud as it should be.


Then you have a serious problem with the amp. The amp can't work without the PI, unless there is a short circuit. You need to pull the chassis and have a look at the circuit. Maybe a wire or component is across the PI tube socket connections? :?:

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Post subject: Re: Fender excelsior lost power
Posted: Tue Sep 24, 2013 3:26 pm
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shimmilou wrote:
jdawgsmusic wrote:
if i remove V1 amp quits completely. But, as I said before, With V2 tube in or out make no difference at all. Amp is about half as loud as it should be.


Then you have a serious problem with the amp. The amp can't work without the PI, unless there is a short circuit. You need to pull the chassis and have a look at the circuit. Maybe a wire or component is across the PI tube socket connections? :?:


+1

This is the only full schematic I could find. V2B is definitely the PI. Given that there are only two 12AX7s in the amp and all four sections are used, any way you divide them up will cause the amp to stop passing the guitar signal if either tube is removed. So, either there is a very serious problem with the amp or the OP does not know which tube is which.

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Post subject: Re: Fender excelsior lost power
Posted: Tue Sep 24, 2013 6:53 pm
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Bill, I know this is going sound silly, but... that Excelsior has a concertina phase inverter. If I remember correctly, you can have signal (albeit attenuated by that 1 meg-ohm grid-to-ground resistor) pass thru the PI stage (minus the tube) and into the lower 6V6GT.

The amp would be forced into single-ended topo, but you can get a faint signal coming out of the speakers. Very distorted and muted. I goot try this out with my Princeton Reverb. The only other amp that I know of that uses the concertina PI.

Told you, it's going to sound silly. :lol:


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Post subject: Re: Fender excelsior lost power
Posted: Tue Sep 24, 2013 9:44 pm
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BMW2002Ti wrote:
Bill, I know this is going sound silly, but... that Excelsior has a concertina phase inverter. If I remember correctly, you can have signal (albeit attenuated by that 1 meg-ohm grid-to-ground resistor) pass thru the PI stage (minus the tube) and into the lower 6V6GT.

The amp would be forced into single-ended topo, but you can get a faint signal coming out of the speakers. Very distorted and muted. I goot try this out with my Princeton Reverb. The only other amp that I know of that uses the concertina PI.

Told you, it's going to sound silly. :lol:


Well, looking at the schematic, you may be right. The OP says that it makes no difference in sound if V2 is pulled or not, so it sounds like V2 may be bad. The OP doesn't say if he actually tried a new tube in V2. :idea:

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Post subject: Re: Fender excelsior lost power
Posted: Wed Sep 25, 2013 3:43 am
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BMW2002Ti wrote:
...you can have signal (albeit attenuated by that 1 meg-ohm grid-to-ground resistor) pass thru the PI stage...a faint signal coming out of the speakers. Very distorted and muted...


The signal would still go to ground before it would go to the output tubes, all signal dumped across the 1 meg (+56K), unless there was a path of less resistance, ie through the PI. :?:

If you could hear any output at all it would be more like you've described, very faint and distorted, with the volume all of the way up, not nearly half power as the OP described.

The OP did say that he put in new tubes, but didn't specify all tubes.

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Post subject: Re: Fender excelsior lost power
Posted: Sat Aug 30, 2014 7:04 am
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Yes the amp will work with V2 removed! This is perfectly normal and does not indicate a serious problem as somebody stated earlier. Look at the schematic!

http://ampgarage.com/forum/files/pawnshop_excelsior_schematic_149.pdf

When V2 is not working for whatever reason (I'll come to that later), The (signal from your preamp (V1) will reach one of the power tubes via R25 (1M). Together with R26 (56k) the two resistors make a Voltage divider that strongly attenuates the signal and while signal from preamp has a high impedance, probably C22 bleeds off highs to ground. So... there you have it: low power (attenuated preamp signal only reaching one of the two power tubes) with little sparkle (highs bleed off). The second hint is that your tremolo (2nd triode in V2) isn't working. Conclusion, both triodes of V2 aren't working.

It is very obvious your V2 has a problem. First plug in a fresh ECC83 and try again. It is strange though that both triodes have a defect. It's also not like components around both triode circuit have a problem at the same so my guess is there is a problem with the 6.3V filament Voltage (look closely at the tube, it probably isn't glowing).

The 6.3 filament Voltage comes from below and while V1 seems to be working fine, the 6.3V seems to be present in the upper deck. Check pins 2 and 7 on V2 socket. Probably one of the wires is loose or has a bad solder. It must be something like that. If you're not familiar working on tube amps, visit your local tech. This should be an easy fix.


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