pacificaudiomagnetics.com

[Helmholtz]

I wouldn't buy a 50W Plexi OT having an Raa of 4.5K or a JTM45 OT with an Raa of 10.4k (??).

[nosaj]

Edcors version of an EL84 PP output (XPP25-7.6K - 25W) costs less than half the PAM model (PAM-OT-18-31R)

$57.77 vs $124.88, and the Edcor includes 40% screen taps...

And blue is Cooler!
nosaj

[mozz]

I wouldn't buy a 50W Plexi OT having an Raa of 4.5K or a JTM45 OT with an Raa of 10.4k (??).

Some of the Fender values were also odd, 12k?

[Chuck H]

Edcors version of an EL84 PP output (XPP25-7.6K - 25W) costs less than half the PAM model (PAM-OT-18-31R)

$57.77 vs $124.88, and the Edcor includes 40% screen taps...

I've had great results from Edcor products. But the last time I ordered a part from them it was a single OT. Their shipping charge minimum policy at that time made it a little more expensive than many alternatives (shipping considered). So there's that. I don't know about their current shipping policy but if it hasn't changed then they're not engaging the DIY market effectively.

JM2C

EDIT: Well I only now looked at the two transformers in question. What I'll offer in PAM's defense is that their product looks to be a replica for fit and materials. Which is more trouble than the plastic bobbin Edcor unit. That said, I have nothing against modern construction methods and the last OT I got from Edcor sounded great. But for some that vintage aesthetic is worth paying more.

EDIT 2: After perusing the PAM site I did find their "Red Series" products which might be modern construction transformers like the Edcor products. Or not. The site says they're made with the same materials and processes as their Vintage Replica line except that they're made in Asia instead of the US. PAM does offer a 20W 8k/8ohm OT for a reasonable price in the Red Series. After calculating shipping I found that you can get the PAM OT for $57.40 where the linked Edcor OT (because of their expensive shipping) would be $86.77.

[Greg_L]

There's a local amp company here called Steamboat. They seem to use and prefer a lot of Edcor transformers. Not sure why, maybe they have a deal with them, I don't know. But the Steamboat stuff seems pretty cool and very well built.

[Chuck H]

There's a local amp company here called Steamboat. They seem to use and prefer a lot of Edcor transformers. Not sure why, maybe they have a deal with them, I don't know. But the Steamboat stuff seems pretty cool and very well built.

Edcors high shipping rate applies to single units or small quantities of lighter models. I guess they don't offer USPS, just Fed Ex, and a minimum charge for three pounds. At least that's what they told me when I asked why their shipping cost so damn much. Point is that I'm sure multiple and heavier units makes their shipping more reasonable.

[Chuck H]

I wouldn't buy a 50W Plexi OT having an Raa of 4.5K or a JTM45 OT with an Raa of 10.4k (??).

Not to mention a Traiwreck Express OT at 7.5k Raa.?. This is for a pair of EL34's. The reported Raa for the Express from the original Stancor units is 6.6k. Someone that knew Ken very well has reported that different OT specs for later Express amps is just hype and never actually happened. Alternate manufacturers OT's used when the Stancor A3801 became unavailable were spec'd for 6.6k. It's reported that only one or two Express amps were made with Pacific OT's. I have to assume they were spec'd at 6.6k. I've also read at the Amp Garage (these guys know their Wreck lore) that the current Pacific iron is not like the old iron at all. So I wonder where these odd and incorrect primary impedances are coming from in the PAM line.

[Greg_L]

Not to mention a Traiwreck Express OT at 7.5k Raa.?. This is for a pair of EL34's. The reported Raa for the Express from the original Stancor units is 6.6k. Someone that knew Ken very well has reported that different OT specs for later Express amps is just hype and never actually happened. Alternate manufacturers OT's used when the Stancor A3801 became unavailable were spec'd for 6.6k. It's reported that only one or two Express amps were made with Pacific OT's. I have to assume they were spec'd at 6.6k. I've also read at the Amp Garage (these guys know their Wreck lore) that the current Pacific iron is not like the old iron at all. So I wonder where these odd and incorrect primary impedances are coming from in the PAM line.

In general, is that enough of a primary difference to make an actually audible difference?

[Helmholtz]

In general, is that enough of a primary difference to make an actually audible difference?

Acc. to Prof. Zollner and the GITEC guys, the most audible differences (based on direct switching tests) between OTs are caused by different primary impedance.

[SoulFetish]

Im wondering if those numbers listed on the spec sheet are a mistake. The only way those make any sense is if the person creating the drawing thought that the actual p-p impedance was for one half of the winding and doubled it, or simply copied and pasted the specs to wrong model number.
Certainly, you can apply a fairly wide range of platr loads by making adjustments to the screen voltage and grid bias, so the tube work in their safe operating range.
But that spec for a JTM 45 makes no sense at all

[Helmholtz]

Even an Raa of 6.6k with a pair of EL34s is borderline.
The situation is comparable to a JTM 45 using an Raa of 8k with a pair of KT66s.

In both cases the Raa is about twice the optimal load (assuming plate and screen voltages around 400V).
Results are lower power output, large screen currents, reduced plate dissipation and more compression before clipping (which might be desirable).

[Greg_L]

Acc. to Prof. Zollner and the GITEC guys, the most audible differences (based on direct switching tests) between OTs are caused by different primary impedance.

Ok but does a +/- 1k impedance difference on the primary of an OT make enough of a difference to worry about when comparing to what we *think* vintage pieces sounded like when new themselves?

My point being, like I get into these conversations with people sometimes....they want an amp that sounds like a factory correct 59 Bassman, and I'm like...do you really even know what that sounds like? We know what they sound like now...65 years later. Some people probably remember them from the 70s and 80s. Who really remembers what they sounded like brand new? I think sometimes people stress over the minutia of things that don't really matter and lose focus on what does - just playing the amp.

[Chuck H]

Ok but does a +/- 1k impedance difference on the primary of an OT make enough of a difference to worry about when comparing to what we *think* vintage pieces sounded like when new themselves?

My point being, like I get into these conversations with people sometimes....they want an amp that sounds like a factory correct 59 Bassman, and I'm like...do you really even know what that sounds like? We know what they sound like now...65 years later. Some people probably remember them from the 70s and 80s. Who really remembers what they sounded like brand new? I think sometimes people stress over the minutia of things that don't really matter and lose focus on what does - just playing the amp.

Well the issue apart from tone still remains. Where 1k can absolutely make a difference. As noted by Helmholtz 6.6k at 400V (I think the TW Express is between 410V and 420V) is already borderline. Increase the Raa from there and it's probable the screens will over dissipate. So there's something wrong then if PAM is marketing an OT with an Raa of 7.5k specifically for an amp that is pretty much intended to be cranked all the time and uses a pair of el34's at 420Vp. Right?

[Helmholtz]

My point is that I can't trust a company selling replacement parts having wrong specs.
Either they don't care or they don't know how to measure their results.
It shouldn't be a problem to adjust the winding machines for the correct number of turns (provided they cared to find out).

[Helmholtz]

My point being, like I get into these conversations with people sometimes....they want an amp that sounds like a factory correct 59 Bassman, and I'm like...do you really even know what that sounds like? We know what they sound like now...65 years later.

Turns' ratio doesn't change with age.