Excelsior loses volume after warming up

Wally

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465.5ohms…… That indicates that those two 270ohm resistors are running in series. Those tubes are running at about 84% of max plate dissipation.

EDIT: I am in error here. Without the schematic I took for granted that you were looking at the bias resistance circuit. Apologies.
 
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corliss1

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No - Deoxit is not the appropriate cleaner for those type of connections. The most common Deoxit we talk about is D5, which is also a lubricant, which isn't what we want on those contacts. I doubt any of the slip on things need to get cleaned - you can just squish them a little bit extra with some pliers once they're on if that makes you feel better.
 

peteb

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screefer

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The 270s are in the power supply.
Roger.
Thanks for the link.
Earlier I described the cathode resistor as the bias resistor which of course, I now see, are the same.

So looking at the schematic, r22 and r30 are the 270s. What is their function?
In my very limited knowledge r58 and r59 would be the dropping resistors?
On a 5e3 schematic, I don't see any resistors but the droppers before the filter caps??

Back to the books and the great link you sent me.
 

corliss1

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R22 and 30 are dropping resistors in the power supply.

58 and 59 are between each filter capacitor. They help isolate each filter stage, with values also chosen for voltage drops.
 

screefer

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R22 and 30 are dropping resistors in the power supply.
Thank you Corliss

So enough of this. I clearly need to study up. I now have the schematic and the board is clearly marked (layout).
I have enough to research further. I'm in 'old dog, new tricks' territory and can only ask so much.
You all have been tops! :)
Cheers
 

Dacious

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On the s/h Excelsior I owned it worked for 20 minutes then fizzled out. After a half hour it'd fire up again.

The guy before had been tube rolling. These are a 6V6 Tremolux with a MOSFET driving the tremolo instead of a tube. He'd used some NOS or old pull 12AX7 that position and it was blackened. A 12AT7 fixed it but it lost a lot of balls. 12AX7 is the go but you need the right one

Otherwise, it's a 5E3. Cathode biased with a cathodyne inverter. If you run most modern and even some old long plate tubes in V2 you'll cook the grid. That was the problem with mine. I slapped a Shuguang aka Ruby aka Marshall tube in there. Short plate tube with the shiny E in it.

End of problem. That's the reason Marshall uses them in their amps with cathode followers and Mesa uses JJs usually on V3 or V4 depending on the amp. I have had a couple of Shuguang that didn't live but mostly they're tough as nails.

I have a feeling there's some big ass cement bath resistors used as sag resistors off the hi voltage rectifier diodes but I'm going on memory here.
 
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peteb

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They are simulating the response of a vacuum tube rectifier, probably a 5Y3.
Good call NTC. That looks right.

why would they place one resistor on each ‘leg’ of the rectifier.

they could use one resistor downstream of where the two legs join together.

one component instead of two
less chassis space used.
two fewer electrical connections

they could have saved big bucks.
 

screefer

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On the s/h Excelsior I owned it worked for 20 minutes then fizzled out. After a half hour it'd fire up again.
All was good with the new tubes in when, again, it wouldn't power up. I removed all the spade terminals from the switch and tested continuity on switch and all was good. I popped the terminals back on and it fired up.
I then went to play and immediately the volume fizzled. I shut it off and removed the 6V6S power tubes and they looked OK. I put them back and no change. I then went to observe all tubes under these conditions, so with the volume down I removed the shields on V1&2 and right away it worked!! It has kept working fine since yesterday through 3-4 power ups and downs so, being curious, I popped the old 6v6s back in and it has now been on for over an hour and working fine. I must say that the JJs sound noticeably better. This amp is dead quiet until 2 o'clock on the dial but that is way too loud for my purposes. Turning it to 12 o'clock and using V on the guit works but 8:30-9 is fine. I have the tone control in the 'middle' position and alternate between the guit. and acc. inputs.
My acoustic Yamaha APX600 tuned to open G with slide is surprisingly satisfying.

If it pooches again, My plan is to first chopstick (with amp on) and then examine all spade terminal connections (with amp off and drained) and then maybe reflow all solder connections on the power board.

Thanks again for all the input. I have a schematic. It's a cheap amp (that sounds great!) and there could be lots of gremlins lurking. I'll learn something by chasing them!!

Cheers
 

NTC

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Good call NTC. That looks right.

why would they place one resistor on each ‘leg’ of the rectifier.

they could use one resistor downstream of where the two legs join together.

one component instead of two
less chassis space used.
two fewer electrical connections

they could have saved big bucks.
Maybe not. If they used one resistor, it would probably be the same value but would have to be twice the rated power. 2x 10W at twice the quantity may very well cost less than 1x 25W resistor. It may have been a space consideration as well, but I doubt it as there seems to be plenty of room there either way - though THAT could also play into how many boards they got per panel (don't ask!).

Have you looked closely at the socket pins? Did you try to tighten them? I keep thinking that could have something to do with it. The shields may be pushing one or both tubes such that it makes poor contact and it gets worse as things heat up.
 

screefer

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I will note that. I did remove Vs 1&2 and they were a very snug fit when I put them back but there could be one pin socket that is not tight. I do have JJ replacements for them on order. I'm expert at removing the chassis and will inspect the sockets when the Vs arrive OR before if things revert.
 

Wally

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All was good with the new tubes in when, again, it wouldn't power up. I removed all the spade terminals from the switch and tested continuity on switch and all was good. I popped the terminals back on and it fired up.
I then went to play and immediately the volume fizzled. I shut it off and removed the 6V6S power tubes and they looked OK. I put them back and no change. I then went to observe all tubes under these conditions, so with the volume down I removed the shields on V1&2 and right away it worked!! It has kept working fine since yesterday through 3-4 power ups and downs so, being curious, I popped the old 6v6s back in and it has now been on for over an hour and working fine. I must say that the JJs sound noticeably better. This amp is dead quiet until 2 o'clock on the dial but that is way too loud for my purposes. Turning it to 12 o'clock and using V on the guit works but 8:30-9 is fine. I have the tone control in the 'middle' position and alternate between the guit. and acc. inputs.
My acoustic Yamaha APX600 tuned to open G with slide is surprisingly satisfying.

If it pooches again, My plan is to first chopstick (with amp on) and then examine all spade terminal connections (with amp off and drained) and then maybe reflow all solder connections on the power board.

Thanks again for all the input. I have a schematic. It's a cheap amp (that sounds great!) and there could be lots of gremlins lurking. I'll learn something by chasing them!!

Cheers

I am going to guess that the heaters in the preamp are failing. I would retension those sockets and reflow the solder joints on the heaters.
 

Dacious

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The Excelsior board, and tube sockets mounted on the chassis on fly leads, is exceptionally tough. Blues and Horrid Deluxe and Juniors can only dream of such a sturdy board.

Nice thick traces. Probably depleted uranium..... but like out of a tank. Plus ceramic sockets. The tube shields are chintzy crap and yes could even be cocking the tube crooked in the socket which could be causing a futz-out. The shield base dimples wear out in nothing flat. Belton shields and sleeves fit

the PCB and nice meaty transformers make up for the cheap fittings elsewhere - considering the price though - it's better than many name amps for construction. Great mod platform, tons of room. I have a Fender Greta that is the same. Chintzy cabinet housing rock solid transformers and PCB well overspecified. With a nos Sharp 5" alnico radio speaker and National 12AX7 and 12AT7 tubes it's an awesome breakfast bar amp great for noodling.

There's a guy in NZ been running his Excelsior on 6L6s. I tried it, just lost that 6V6 character with slight increase to headroom but neither transformer ran hot despite impedance mismatch on the output.

i was even going to make a ply cabinet to lighten mine but someone made me an offer I couldn't refuse for it. If another turns up I'd snap it up.

Heres my mod thread with footswitch and dwell for trem, tone control. Definitely gig worthy.
 
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