I hate cheaply made transformers!!!

glassman

glassman

Electron Herder
So I get this early production Peavey 5150 in my shop for a low power complaint and to add a bias adjustment. I bench it and run it through its paces and determine that half of the power section is not contributing, so I measure the OPT with my multimeter...24% mismatch DC resistance...I assumed it was bad but since I never measure OPTs with DC resistance I threw it on the LCR bridge and found that both the inductance and impedance at 1000 cycles were within 0.1% of each other, side to side! So we have a "good" OPT with a massive DC mismatch...each side draws a different current and biasing ends up being nothing more than an approximation.

Sorry about the rant...
 
Re: I hate cheaply made transformers!!!

That is a good rant.....I don't know the technical side well enough to be aware of something like that. Good to know that can happen. Thanks.
 
Re: I hate cheaply made transformers!!!

the guy who invented fire said:
Not surprised at all!

Im not one of those transformer snobs but good transformers do go a long way to getting a good amp!
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I'm not a transformer snob either...and I totally agree with you about the transformer being a key factor in a good amp. The "stock replacement" transformers I keep in stock vary between less than 1% DC mismatch and about 4%; these are standard value replacements, not the high end stuff. I find this level of mismatch acceptable as the originals generally had the same tolerances. My 20 years on the quality/application engineering side of the magnet wire industry leads me to understand that to get a 24% DC mismatch, some serious corners had to be cut. It's just disappointing that these "children of a lesser god" make it into anything but the cheapest tube electronics.
 
Re: I hate cheaply made transformers!!!

glassman said:
I'm not a transformer snob either...and I totally agree with you about the transformer being a key factor in a good amp. The "stock replacement" transformers I keep in stock vary between less than 1% DC mismatch and about 4%; these are standard value replacements, not the high end stuff. I find this level of mismatch acceptable as the originals generally had the same tolerances. My 20 years on the quality/application engineering side of the magnet wire industry leads me to understand that to get a 24% DC mismatch, some serious corners had to be cut. It's just disappointing that these "children of a lesser god" make it into anything but the cheapest tube electronics.
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That might explain why I never liked alot of the Peavey product..
 
Re: I hate cheaply made transformers!!!

STRATDELUXER97 said:
That might explain why I never liked alot of the Peavey product..
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also explains why hot-rodded 5150s with aftermarket OTs can sound flat out amazing compared to the out-of-the-box amps. the factory guts are :thumbsdow
 
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Re: I hate cheaply made transformers!!!

CaughtLikeFire said:
also explains why hot-rodded 5150s with aftermarket OTs can sound flat out amazing compared to the out-of-the-box amps. the factory guts are :thumbsdow
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Maybe so....I always felt the 5150 was too ("mosquitos buzzing) in the preamp though...Alot of people didn't realize that the 5150,the SLO 100,and the early Mesa Dual Rec preamps were almost identical...Basically they copied Soldano's preamp...Those that work on,mod amps,and have the schematics,would see this...

I was always surprided that Soldano didn't sue the companies,or maybe he just didn't have a patent on his preamp at the time?

All 3 preamps are scaringly close! Coincidence ya think?
 
Re: I hate cheaply made transformers!!!

STRATDELUXER97 said:
I was always surprided that Soldano didn't sue the companies,or maybe he just didn't have a patent on his preamp at the time?
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Pretty hard to get IP protection on those types of circuits. Besides, getting to the original topic, a lot of the magic in the SLO is from the DeYoung tranny.
 
Re: I hate cheaply made transformers!!!

aleclee said:
Pretty hard to get IP protection on those types of circuits. Besides, getting to the original topic, a lot of the magic in the SLO is from the DeYoung tranny.
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The original topic was about cheap Peavey early 5150 transformers...No mention of the Soldano,until I mentioned it..:1:
 
Re: I hate cheaply made transformers!!!

STRATDELUXER97 said:
The original topic was about cheap Peavey early 5150 transformers...No mention of the Soldano,until I mentioned it..:1:
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Depending on how you look at it, it could be about the difference that good trannies make in an amp's tone. ;)
 
Re: I hate cheaply made transformers!!!

glassman said:
I'm not a transformer snob either...and I totally agree with you about the transformer being a key factor in a good amp. The "stock replacement" transformers I keep in stock vary between less than 1% DC mismatch and about 4%; these are standard value replacements, not the high end stuff. I find this level of mismatch acceptable as the originals generally had the same tolerances. My 20 years on the quality/application engineering side of the magnet wire industry leads me to understand that to get a 24% DC mismatch, some serious corners had to be cut. It's just disappointing that these "children of a lesser god" make it into anything but the cheapest tube electronics.
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What would have to happen so that one side of the OT primary would be 25% higher/lower DC resistance than the other?
Thank You
 
Re: I hate cheaply made transformers!!!

My guess is:

A) using poor quality transformers [IE, the quality control wasn't very good]
B) a power outtage/blackout
C) turning on the amp wrong [IE, standby switch then power]
D) someone very annoyingly unplugged the **** cord with the amp turned on. But I think this would only mess up some fuses; not sure of the long term effects [I'm sure there are some, though].

Lastly, it could just be that they are going out. Then again, I'm just kinda going based on logic and not experience with this, so no one has to listen to me.
 
Re: I hate cheaply made transformers!!!

zzmoore said:
What would have to happen so that one side of the OT primary would be 25% higher/lower DC resistance than the other?
Thank You
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The transformer in question would have had to of been "successively wound". In more simplistic terms, the individual windings of the primary and secondary are wound one at a time; in the case of the primary winding, both sides would have the same number of turns, but the portion wound second would have a larger radius, corresponding to a longer wire length and greater resistance. This wouldn't affect the AC characteristics of the transformer directly but would affect the DC characteristics of the output tubes.

My best guess, based on the measured values, would be that the secondary was wound between the two sides of the primary. This is common practice for power transformers when space is at a premium within the lamination. The smaller wire of the primary (in this case) is easier to manipulate to fit in a tight place.

The preferred method of winding an output tranny is to wind the two sides of the primary simutaniously so that the total length of the wire is as close as possible to the same length on both sides.
 
Re: I hate cheaply made transformers!!!

STRATDELUXER97 said:
All 3 preamps are scaringly close! Coincidence ya think?
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I have a feeling you were asking rhetorically, but if not in the 5150 case EVH was very into Soldanos and then signed the amp deal with Peavey. A short and easy to follow crumb trail....
 
Re: I hate cheaply made transformers!!!

Yes, he was very into Soldanos and used a SLO for much the Carnel Knowlege record. I recall from interviews that while he liked the SLO he disliked the what he termed the "slow response" of the amp. I think this was in reference to transient attack. The 5150, he said, was a SLO but with "faster response" to the pick attack.
 
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