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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Tue Sep 13, 2016 1:09 pm
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"While I believe a small increment change in the power dropping resistors will lower the voltages at its given stage, I have to go with my gut at this point. Incorrect high filament and plate voltages are a direct result of the power transformer being out of spec....."

sfceric64, but in a 60 year old tranny --- I have never seen the spec = too high voltage. UNLESS it is the wrong PT. Is there a Fender part number? If this is the correct PT for that amp and you buy a new one --- you will almost for sure have high voltages.

Before you buy another PT. Pull all the leads. Leave the primary side attached with fuse. Now, measure the secondary side VAC (ends to CT). Including the 5VAC and filament leads. Not sure if you've done this already... but post numbers, when you get them. Be sure to measure outlet voltage at the time of the readings.

Good luck!


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Tue Sep 13, 2016 3:19 pm
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There are no markings on the PT other than the Triad sticker & #.
The only CT is located on the primary side, Red-Red/Yellow-Red.
The secondary consists of a pair of Greens and a pair of Browns.
The transformer was wired correctly to the rectifier, fuse and on/off switch with the Red/Yellow and one Green to chassis ground.
The input voltage was 120, while the output was measured at 362Vac.
The Green measured 6.57Vac to the lamp and tube heaters.
The Brown measured 5.25Vac and 7.25Vac to the Rectifier Filaments.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Tue Sep 13, 2016 4:47 pm
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sfceric64 wrote:
The input voltage was 120, while the output was measured at 362Vac.
The Green measured 6.57Vac to the lamp and tube heaters.
The Brown measured 5.25Vac and 7.25Vac to the Rectifier Filaments.


Those specs *seem* consistent for a tweed Deluxe P/T.

Arjay

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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Tue Sep 13, 2016 4:53 pm
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sfceric64 wrote:
There are no markings on the PT other than the Triad sticker & #.
The only CT is located on the primary side, Red-Red/Yellow-Red.

The secondary consists of a pair of Greens and a pair of Browns.

The transformer was wired correctly to the rectifier, fuse and on/off switch with the Red/Yellow and one Green to chassis ground.


Little confused here. The primary side should be two black wires. The HV secondary is Red/Red-yellow/Red. With red-yellow being the CT.

Green lines are the filaments. Your amp only has one line to the heater. The other green line is grounded. The Brown wires are prolly yellow (for rectifier, 5VAC)?

sfceric64 wrote:
The input voltage was 120, while the output was measured at 362Vac.

The Green measured 6.57Vac to the lamp and tube heaters.

The Brown measured 5.25Vac and 7.25Vac to the Rectifier Filaments.


All voltages seem ok. Not too crazy. Just out of curiosity, what filter cap mfd did you place into the PSU? 20mfd/500VDC F&T caps? Were the OEM 16mfd? An increase in mfd can raise the voltage on the tap points.

Too bad you don't have access to another PT... as I am not sure the PT is the problem. 360VDC on those 6V6GT is not bad. But, the excessive voltage on the 6SC7 anodes maybe causing overdrive issues. Do you have a 12K or 15k-ohm, 5-watt resistor you could sub into the 10K-ohm position?


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Tue Sep 13, 2016 7:01 pm
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This is the only confusion, the rest is just my lack of proper terminology between primary/secondary.
Quote:
360VDC on those 6V6GT is not bad. But, the excessive voltage on the 6SC7 anodes maybe causing overdrive issues.
The output transformer red wires are supplying 362VAC to the rectifier supply side and 7.25VAC to one of the filaments of the rectifier. The 6v6 plates are getting 349/347 after taking out the cathode voltage(the layout calls for 280). You don't think the 7.25 volts to one side of the rectifier filament is to high(40%) over the called for 5V?

The brown wires probably were yellow at one time.
The filter caps are OEM Sprague 20mfd 450V, F&T as far as I've seen doesn't do 20's.

Quote:
Too bad you don't have access to another PT
I will as soon as one gets delivered. I also plan on getting a various assortment of 12-18k 3 watt dropping resistors to sub into the circuit.

I may get the old triad a spot on the mantle until I can send it off to get rewired.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Tue Sep 13, 2016 7:32 pm
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sfceric64 wrote:
This is the only confusion, the rest is just my lack of proper terminology between primary/secondary.

The output transformer red wires are supplying 362VAC to the rectifier supply side and 7.25VAC to one of the filaments of the rectifier. The 6v6 plates are getting 349/347 after taking out the cathode voltage(the layout calls for 280). You don't think the 7.25 volts to one side of the rectifier filament is to high(40%) over the called for 5V?


OK. We have a nomenclature problem. There are two main transformers in most amps. A power transformer (PT) and an output transformer (OT or OPT). The PT supplies high voltage AC to the amp. The OPT drives the speakers.

Now, every transformer has two "sides." A primary winding side and a secondary side. The purpose is to change the voltage from one level to another level via the specific number of winds in each side. What we are talking about in your amp (at the moment) is the PT.

The primary side of the PT is hooked to the house AC outlet. The secondary side has an HV AC output hooked to the rectifier (several hundred VAC). Separate windings for the heater lines of the tubes (6.3 VAC). And a pair of lines to heat the filament or cathode of the rectifier (5VAC).

As for balance of VAC you read... you are reading without any load. Once the heater filaments are loaded onto the PT and the unit is playing at volume ---- my bet is the voltage will balance out. In any event, it is not that critical, as the function is only to heat the filaments. Higher voltage may reduce the tube's life. But, should not affect the tube's performance --- as much as too much voltage on the anodes.

As for too high voltage on the plates... This is prolly not a PT issue. Too much voltage is a PSU issue. To drop the voltage would require playing with the rectifier and dropping resistors. Or putting another dropping resistor inline with the first filter stage... to drop the B+.

I would not do this, unless you are getting adverse tonal effect specifically due to high plate voltages. Remember, you can drop the voltages onto the 6SC7 independent of the 6V6GT. I'd do this first and listen to the results. You need to determine what stage is being overdriven. Is it the gain stages or the output. And adjust the voltages accordingly.

If you must reduce the 6V6GT idle bias... do it by changing the cathode-tied resistor and/or the grid-to-ground resistor first. I would avoid major changes to the PSU. As this can result in adding more problems to the mix.

Good luck! Keep us informed.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Wed Sep 14, 2016 8:11 am
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The heart was removed from the amp and it is now relegated to the most expensive piece of art I own.
The icing on the worst August in fifteen years.
I don't expect to attempt recovery for some time.
SNAFU
BLNT


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Wed Sep 14, 2016 10:21 am
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What happened?

I don't think the amp is far from working fine. I don't believe you need any transformers. Which tends to be the most $$$ part.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Thu Sep 15, 2016 10:37 am
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Well, all I can say at this point in the journey is this. If your fortunate enough to find an old amp that you like, you could probably build it yourself from scratch cheaper than trying to repair whatever may be wrong with it.
There are far to many variables that can make it a bad purchase vs the perceived value. I estimated the perceived value of a 1950 Deluxe at about $25. I purchased mine for $15, w/ $5 allotted for repair. As it stands now, I busted my budget and am nearly at my perceived value. It just isn't good economic sense considering a new 57' re-issue deluxe is about $20.
Many of the small changes made had little or no impact. When I get the power transformer re-wound, I will be able to start this journey again and most likely will have to make minor value changes based on the substitutions I've already made.
As to my comments about my worst August in 15 years, its personal and I unfortunately was just venting frustration. Some about the amp and 95% not about the amp or anyone who has read or contributed to the thread.
Thanks for all the help to those that contributed.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Thu Sep 15, 2016 11:23 am
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sfceric64 wrote:
Well, all I can say at this point in the journey is this. If your fortunate enough to find an old amp that you like, you could probably build it yourself from scratch cheaper than trying to repair whatever may be wrong with it.


I sense your frustration Eric, I really do. And perhaps this particular project was too far gone for cost-effective salvation. But I and several others here have been at this for a while and we've achieved a pretty good batting average by choosing our battles wisely based on the level of repair/restoration required and our various skill levels. Maybe you bit off more than you could comfortably chew on your first attempt but don't despair -- a more promising project may come along and you'll have accumulated a lot of knowledge from this exercise that will better prepare you to both assess its potential and deal with the nuts and bolts of successfully resurrecting a relic. Hang in there, sarge.

Arjay

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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Thu Sep 15, 2016 1:57 pm
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Maybe you bit off more than you could comfortably chew on your first attempt but don't despair
I can chew with the best of them, but I'll admit the swallowing hasn't been as easy as I'd hoped.
Just got the quote from Mercury, 4 or 5 week turn around.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Thu Sep 15, 2016 3:19 pm
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Four to five weeks isn't bad -- about what you could reasonably expect for a custom winder, whether tranny or pickup.

At least you'll be certain that the sumbitch is wound to specs.

Arjay

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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Thu Sep 15, 2016 5:07 pm
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Four to five weeks is great turn-around time. As MM is not really setup to do individual PT re-windings, like some other outlets. Even Heyboer, that does a lot of rewinds... takes a good month.

I know frustration with amps and cars. Sometimes, it's best to just step away for a bit. Recharge the mental batteries.

Good luck!


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Sat Sep 17, 2016 6:44 pm
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Yeah, not a disappointing turn around time at all.
Was just stating a timeline; the cost is more than I anticipated but it will be quality work, guaranteed.


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Post subject: Re: Trying to buy my 1st Vintage Amp
Posted: Mon Sep 19, 2016 1:30 am
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BMW2002Ti wrote:
I know frustration with amps and cars.


You're preaching to the choir.

After more than a year I'm still searching for the correct headliner material for my '69 Chevelle!

:lol:

Arjay

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