Most likely the most insane question you'll ever hear...

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Abstract
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Most likely the most insane question you'll ever hear...

Post by Abstract » Wed Mar 07, 2012 6:27 pm

Stick with me...

There's a dud(e) on HCAF...I know, it gets better...who's telling people who are looking to bring the volume down on their amps, to stick a rectifier tube or two into some of the power tube slots.

Seems like a really bad idea.

But I don't know enough about amps to definitively state that that would harm/help/whatever the amp.

http://acapella.harmony-central.com/sho ... ge-in-half!




Thoughts (besides "don't take advice from HCAF") ?


I'll hang up now and wait for an answer. ;)
drhulsey wrote:There are just too many cool things in this world for one life. Thank God for reincarnation 8)

MCK
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Re: Most likely the most insane question you'll ever hear...

Post by MCK » Wed Mar 07, 2012 6:54 pm

Its a hilarious thread! Thanks for making my day...

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milkyBK370
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Re: Most likely the most insane question you'll ever hear...

Post by milkyBK370 » Wed Mar 07, 2012 8:43 pm

That was a good read. Had me in stitches.

MCK
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Re: Most likely the most insane question you'll ever hear...

Post by MCK » Wed Mar 07, 2012 8:57 pm

It reads like a page off the Dumb & Dumber movie sequel. Too bad we never found out what it costed Ricky Bobby to get his amp repaired.

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NickC
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Re: Most likely the most insane question you'll ever hear...

Post by NickC » Wed Mar 07, 2012 8:58 pm

Kids!

They walk through Guitar Center on a Saturday ...... play Stairway To Heaven (in spite of the signs saying No Stairway!) at 130db through several Mesa Boogies sporting logos like "Double Rectifier", "Triple Rectifier" ...... and they start to get ideas.

Crazy ideas.

Kids! :wink:

MCK
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Re: Most likely the most insane question you'll ever hear...

Post by MCK » Wed Mar 07, 2012 9:02 pm

Well, amp techs need to make a living right? The world needs all kinds of people! :wink:

Weathered
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Re: Most likely the most insane question you'll ever hear...

Post by Weathered » Wed Mar 07, 2012 10:44 pm

MCK wrote:It reads like a page off the Dumb & Dumber movie sequel. Too bad we never found out what it costed Ricky Bobby to get his amp repaired.
Funny story is that Ricky Bobby is more or less playing with the person on HCAF. He knows better than to do this with an amp....he tends to bat people around over there quite a bit.

MCK
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Re: Most likely the most insane question you'll ever hear...

Post by MCK » Wed Mar 07, 2012 10:54 pm

Weathered wrote:
MCK wrote:It reads like a page off the Dumb & Dumber movie sequel. Too bad we never found out what it costed Ricky Bobby to get his amp repaired.
Funny story is that Ricky Bobby is more or less playing with the person on HCAF. He knows better than to do this with an amp....he tends to bat people around over there quite a bit.
Ah he had me then! I didn't read his other posts etc so I fell for it! Still fun reading.

Abstract
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Re: Most likely the most insane question you'll ever hear...

Post by Abstract » Wed Mar 07, 2012 11:39 pm

OK...so like I'm serious.

What really happens if you do this?
drhulsey wrote:There are just too many cool things in this world for one life. Thank God for reincarnation 8)

Jana
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Re: Most likely the most insane question you'll ever hear...

Post by Jana » Wed Mar 07, 2012 11:48 pm

And people thought I was a dumbass when I drove grandpa's 49 Ford in a river.

What would happen with this?

It depends on how the rest of the circuit is wired up. Let's assume that the 6.3VAC has a center tap that is grounded. If that is the case, then there is 3.1 VAC across pins 2 and 8 of the rectifier tube--probably enough to light it up enough to conduct.

Pin 4 of the rectifier tube is now connected to the screen grid pin. So, a 470 to 1K resistor from pin 4 to the B+ supply for the screens. I would imagine there is now significant current flowing here. Probably sagging the Power supply pretty good (provided the 1K isn't smoking).

How was pin 6 used in this amp? Is it a tie point for the 470 to 1K resistor mentioned above? If so, then there is another path, minus the resistance, for the B+ screen supply.

Both of those paths are to ground--pin 8.

Yup, I can imagine it did reduce the volume of the amp quite a bit. Eventually to a point of no volume!

Any errors in my analysis?

Firestorm
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Re: Most likely the most insane question you'll ever hear...

Post by Firestorm » Thu Mar 08, 2012 2:49 am

I'm not sure the screen resistor will see much more current than usual: Pin 6 current will drop the voltage of the 5U4 plate connected there, which makes the other plate at Pin 4 more attractive, so it's self-limiting.

Basically, it looks like the 5U4 becomes a single diode pushing negative voltage into the screen supply and positive voltage onto the output tube cathode (assuming they share a cathode resistor).

Dropped screen, cold bias, only half the OT primary connected ... it almost could work in a perverse sort of way. Still a really terrible idea.

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rp
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Re: Most likely the most insane question you'll ever hear...

Post by rp » Thu Mar 08, 2012 3:06 am

Hey, I've been known to do this :shock: - By accident! Luckily I can repair my own amps and don't charge myself anything.

What happens? What Jana said, sometimes nothing, sometimes the fuse blows, sometimes you'll smoke a power string resistor.

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M Fowler
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Re: Most likely the most insane question you'll ever hear...

Post by M Fowler » Thu Mar 08, 2012 3:11 am

I had inserted an EL34 in a tube socket one day and the amp didn't work so I looked at the power tubes again and noticed some how I had inserted the index off to the side.

Why do they make tube sockets so loose that you can insert the tube wrong!

It was a Belton socket.

Mark

gingertube
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Re: Most likely the most insane question you'll ever hear...

Post by gingertube » Thu Mar 08, 2012 3:29 am

Abstract,
I take it you really are serious and want to know want might happen!!!!
- So here is a serious consideration of what is likely to happen.

Jana has it mostly right .

1st it IS possible to get lower power by running just one side of a push pull output stage. Generally this will require you adding some sort of "drone" circuit to the side from which you pulled the tube to balance the idle current in the other side - else you will just get really bad hum since the residual power supply ripple is no longer being balanced (cancelled) in the output tranny. The output stage is then thrown into inefficient Class A Single ended operation. Above the level where the driven tube normally transitions into Class AB (the point where the signal is large enough to cause the tube to cut off on the -ve going half of the signal) you would just get seriously bad distortion.

So could the 5U4 provide this balancing idle current? In short NO. The cathode pin of the 5U4, pin 8, is correct, one of the anode pins is pin 4 which maps to the normal 6L6 screen connection, so current could be drawn HOWEVER there is no heater power for the 5U4 and that means no current will flow. Probably just as well else you would end up cooking the screen resistor.

SUMMARY:
It is doubtfull that any damage would result, entirely due to good luck than any sort of judgement.
The result would be very reduced output power with a seriously awful overdrive, amp might be OK at levels 1 to 3 on the volume control.
There will be seriously bad hum - at all levels.

FINAL RECOMMENDATION
Don't do it!!!

Insane? Nah! just garden variety stupid.

Cheers,
Ian

C Moore
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Re: Most likely the most insane question you'll ever hear...

Post by C Moore » Thu Mar 08, 2012 4:58 am

What an IDIOT...!!!
He should have used solid state, silicon, diodes.....not vacuum tube diodes.
Not very experienced I guess.

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