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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Thu Sep 01, 2016 1:00 pm
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Arjay, yeah, I guessed that. But, new stock is as $$$ as old stock... when it comes to 5Y3GT. Several new stock (esp Chinese made ones) --- are relabeled 5Z3P (unique to Communist manufacturers). Some are good. Some not so good. Even as test rectifiers. (IMHO, of course).


https://www.tubedepot.com/products/sovt ... acuum-tube


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Thu Sep 01, 2016 2:24 pm
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I don't mind tossing a chicom-made piece of junk into the trashcan. But it breaks my heart to lose a beloved vintage bottle.

:cry:

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Thu Sep 01, 2016 5:42 pm
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Arjay,

Yes, I know what you mean. Out of principle, better to get a Shuguang or Sovtek tube, for test purposes. Than a 50-60 year old NOS GE. As the GE tube will never be made again.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Thu Sep 01, 2016 6:43 pm
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BMW2002Ti wrote:
As the GE tube will never be made again.


Precisely.

:wink:

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Thu Sep 01, 2016 10:34 pm
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It's just that ppl tend to leave these "test" tubes in units, if they work. And the darn things short out after a few gigs and/or drops.

Remove them after testing & replace with quality rectifiers.

:mrgreen:


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Fri Sep 02, 2016 9:44 am
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BMW2002Ti wrote:
Remove them after testing & replace with quality rectifiers.


Indeed!

Anytime I suspect a HV issue I'll sub out the recto for a GT and throw some 6L6EH's into the final drive while troubleshooting.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Fri Sep 02, 2016 10:51 am
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Well I agree about NOS tubes being better for operations. I hated tossing that 5y3wgta after it shorted, but it happened w/o much notice other than sound waves being destroyed and a little ping that got my attention. You guys, have enough experience that it wouldn't normally happen. Me ahh, NBD learning experience.

The current 5y3gt(NU/59) is holding its own so far, still getting hit w/ excess voltage and the plate is starting to discolor/darken a bit. Its running just over 10% or 388vdc.

I am considering replacing the PT but before I do and to be sure there isn't something I'm missing, I'm going to replace the other resistors and caps w/ the parts I already have on-hand. I know, its not the way it should be done but I don't have the equipment to test everything as needed. So 4 more metal-oxide resistors, 2 metal-film caps(to replace the PIO caps) and 1 Silver-Mica cap(in place of the domino). That will be everything in circuit except the wire/sockets/on-off tone pot/fuse/lamp.
I have looked at Mercury, Hammond and one other I forgot the name of as a new drop in replacement and still looking for a possibly good old P/T reasonably priced. I have found a merit-thordson(sp) that's well priced but may not be a drop in replacement. What would be your wisdom at this point on replacing the P/T?

I ordered replacement AB CC resistors today. Yes, they definitely sound better than metal-oxide; IMO.

Thanks


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Fri Sep 02, 2016 1:12 pm
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These amps do not have grid stopper resistors on the 6V6GT grids. You may need to go to them. Say, usual 1500-ohm, 1/2-watt carbon comp. Like later Fender amps have.

Also, the lack of global negative feedback maybe an issue. I still think the 250k-ohm grid-to-ground resistors maybe a tad too high resistance --- and set the tubes at am idle bias a bit too hot. 220k-ohm or even 180k-ohm G2G combined with the 1500k-ohm grid stoppers may lower bias and stop instabilities. Without too much effect on tone.

These parasitic instabilities can show themselves as excess draw on the rectifier. Just a thought.

If you go the grid stopper route. They MUST be soldered onto the 6V6GT sockets. Short lead length is critical. Fender usually solders the 1500k-ohm resistor across pin 1 (not used) to pin 5 (grid). The signal line re-routes to pin 1. Like photo (the other resistors going from pin 4 to 6 are screen resistors --- I don't think you need them, as there is a dropping resistor in the PSU of your Deluxe) :

Image


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Fri Sep 02, 2016 1:19 pm
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BMW2002Ti wrote:
Also, the lack of global negative feedback maybe an issue. I still think the 250k-ohm grid-to-ground resistors maybe a tad too high resistance --- and set the tubes at am idle bias a bit too hot. 220k-ohm or even 180k-ohm G2G combined with the 1500k-ohm grid stoppers may lower bias and stop instabilities. Without too much effect on tone.


+1

As for power trannies, Heyboer makes some pretty righteous iron that's reasonably priced. And IIRC, Merc-Mag offers re-winds of existing cores (you might consider that if authenticity is preferred).

Arjay

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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Fri Sep 02, 2016 10:23 pm
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Quote:
These parasitic instabilities can show themselves as excess draw on the rectifier
Say what?
Dunno how that could happen if all the electrons are swimming downstream. Are you saying I got a strong swimmer heading upstream? Wouldn't that go to both legs?

Honestly after reading way more than I should, I've got either an older(6450 vs 6452) not quite right PT or a short in a 5v secondary leg w/ most likely the 6.3v secondary pair in the outer windings of the PT.

The newly ordered resistors are all slightly less modern value variants than what is called for.
I don't plan on going to later model mods like 5c3 or BF/SF.
I should get better stability and a closer to right B+ for the circuit w/ a better working PT(it is the first issue I should have addressed) but I thought maybe the out of spec resistors were impacting the whole circuit.
So you think the 250ohm 5w cathode bias resistor is an ok value and the 250k ground resistor should be lowered to 220k to move my voltage 1 volt higher to lower the bias current in the output tubes along with the other grid to ground 250k's? What about the tone stack resistor, lower it to 220k also?

Yeah, I'm getting close to being over budget. I'll never buy anything used that I cant inspect personally again.....
To many scammers/schemers and no-good lying thief's out and about.

Thanks again as always


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Fri Sep 02, 2016 11:26 pm
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sfceric64 wrote:
To many scammers/schemers and no-good lying thief's out and about.


+1

An undesirable consequence of nearly every field of human endeavor.

:evil:

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Sat Sep 03, 2016 7:20 am
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"So you think the 250ohm 5w cathode bias resistor is an ok value and the 250k ground resistor should be lowered to 220k to move my voltage 1 volt higher to lower the bias current in the output tubes along with the other grid to ground 250k's? What about the tone stack resistor, lower it to 220k also?"

Yes. Remember, lower resistance means MORE voltage going to ground, prior to going to grid. A 220k-ohm resistor will DROP the signal voltage being applied to the grids. A 180k-ohm would drop even more voltage.

I'd try the grid stoppers before looking for another power tranny. I really believe you have an instability issue and not unequal AC off the rectifier taps. It's a historic issue. Why almost all amps above 10 watts got grid stoppers in the 1950s.

Check out Randall Aiken's article on grid stoppers:

http://www.aikenamps.com/index.php/grid ... -they-used

Good luck! Keep us posted. :)


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Sat Sep 03, 2016 9:51 am
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Quote:
I'd try the grid stoppers before looking for another power tranny. I really believe you have an instability issue and not unequal AC off the rectifier taps.

There are two 75k grid stoppers(the ordered replacements are 68k) off the board below the 1st/2nd instrument inputs, difficult to see in the photo's from page 6. I've isolated the transformer from the circuit(removed all the tubes) and recorded all Vac. The Vac @ the heaters of V1,V2,V3 & V4 as well as the lamp was the same w/ or w/out the tubes installed 6.6Vac. The Filament voltage of V5 was 4.9 on pin 8 and 6.7 on pin 2. The PT is providing 366Vac to the rectifier via pin 4 and 6. The rectifier is producing 388 Vdc on pin 2 and 8. The rectifier is operating efficiently @.7 (recorded earlier w/ just the rectifier tube in place to determine the B+, etc.

I haven't completed the last bit of work I mentioned yet; V1 grid to ground 5mOhm resistor replacement, tone stack 2.5k and 7k resistor replacement, PIO to metal foil and domino cap to silver mica...

However, the current plate voltage on V2 and especially the output tube plates is high. The bias of V1 and V2 are close to spec. The output tubes are running 34Ma @ idle or 12.845watts. The resulting sound is pure loudness, very clean with the amp volume on two and the guitar on 3 or 4. The speaker is operating fine in this condition. I believe if I pushed it, something will go boom. Likely based strictly on how over the limit the tubes are currently; is the rectifier(as demand increases(to over 400Vdc due to -sig volts) then output tubes(there idling nearly 1 watt over max at idle already) and maybe the OT (just my barely experienced guess here).
The above is why I believe the power supply should be addressed.

There are many ways to skin a cat or play a Strat or wear a hat but when for the love of a new movie will the Cat in the Hat play a Strat.
Sorry but that's what is on my TV, really need to change the channel to college football.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Sat Sep 03, 2016 10:10 am
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"There are two 75k grid stoppers(the ordered replacements are 68k) off the board below the 1st/2nd instrument inputs, difficult to see in the photo's from page 6."

These are the grid stoppers for the input 6SC7.

I am talking about the lack of grid stoppers on your 6V6GT tubes. Check the 5B3 schematic versus the 5E3 schematic. Those 1500 ohm resistors on the 6V6GT grids are there to stabilize the tube and keep them from oscillating. Sudden excessive glowing of the rectifier maybe a sign that the output section is drawing too much current due to instability. Nearly every 6V6GT and 6L6GC Fender amp made from late tweed era forward has these grid stoppers for that reason.

Excessive instability in the output section (6V6GT) almost always leads to fried 6V6GT, rectifier, input and/or output trannies. Instability in the input and gain stages usually do not. In these stages, instabilities = early distortion in volume range & blocking distortion or farting.

http://ampwares.com/schematics/deluxe_5b3.pdf

http://ampwares.com/schematics/deluxe_5e3.pdf

HTH! Good luck.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Sat Sep 03, 2016 10:23 am
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Ok, now I'm on the same page w/ you and see the difference across the schematics. I don't have those sizes on hand in metal-oxide, I'll order a couple pairs. 1 watt enough or do I need two?


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