ClassicTone Customer Service is Excellent!

[bob p]

Just a quick advisory to express my satisfaction with Marvel Electric/Magnetic Components Inc. in supporting their ClassicTone line of trannies. Marvel/MCI is a local company here in Chicago/Schiller Park that supplies American made iron for guitar amp applications.

One of the things that has bothered me somewhat about the ClassicTone line of products is that when using them for a build, sometimes it's hard to get voltages exactly where you expect them to be. For some reason my voltages always turned out higher than I expected. In a conversation I was told that the CT line of iron is always underspec'd and overbuilt. While that's great if you're an engineer/designer who wants to assure that your product meets/exceeds published specs, it's not so great if you're a builder who ends up with higher voltages than you really want.

I recently contacted CT about this problem when comparing different iron for building a Super Reverb clone. I was specifically interested in what type of secondary voltages the transformers would supply under different load conditions. I sent an email to CT over the 4th of July weekend asking for specifics on the 40-18005 power transformer. Much to my amazement, I received an email from the MCI's VP of Engineering, Mark Sacketti, on the morning of July 5 as soon as he returned to work. As soon as he got to work that morning he updated the 40-18005 data sheet to include a load vs. voltage table, published the new data sheet, and sent it to me by email.

Customer service doesn't get better than that.

[bob p]

Product I was asking about:
Fender Power Transformer, Bassman Heads, Bandmaster, Concert, 120V

Spec Sheet:
http://www.classictone.net/40-18005.pdf

Full Disclosure: I have no affiliation with the company. I'm just an end user.

[Randall]

Mark makes the drawings as well.

[big_teee]

I like the Classictone Chokes, & OT's, they sound great.
But, every time I've used their PT's the HT B+ voltages have been way too high.
I'm going to try other brand PTs in the future.
A chart doesn't help, if you can't get the voltages in the parameter ballpark!
The chart on this one isn't even close on my PT.
http://www.classictone.net/40-18016.pdf
I'm done with ClassicTone PTs for a while!

[Stratz]

Whats your average line voltage in your shop/home T?
Mine is ~119v

[Steve A.]

You might try the trick used in my 2002 Mission Amps 5E3 kit: add a zener in series with the PT CT lead to ground to lower the B+.

Steve Ahola

[Tom Phillips]

Is everyone aware that traditional transformer voltage specifications are given for both the rated line voltage and at the rated secondary current load. If the line voltage is high or the load is light (or both) when the measurement is made then you will see a high B+ voltage reading.

[big_teee]

My Line voltage is usually 120V.
The PT manufacturers need to make adjustments for modern voltages.
I think they still wind Transformers like when we had 110V.
On the transformer I listed, I checked it under different load conditions, and while being played.
The B+ voltage never got close to what is on the chart.
We should not have to use Zeners, when the PT is ordered for a paticular type of amp.
My poor Tung-Sol 6V6s will probably have a short life!
T

[bob p]

Is everyone aware that traditional transformer voltage specifications are given for both the rated line voltage and at the rated secondary current load. If the line voltage is high or the load is light (or both) when the measurement is made then you will see a high B+ voltage reading.

Absolutely. Getting the right load is absolutely necessary, and I give ClassicTone a thumbs up for publishing their V = f(load) data. But Terry brings up a good point -- there are manufacturers out there who just clone old transformers by doing forensic unwinds instead of re-designing them to produce the desired performance on today's wall voltages. Mercury is famous for selling obscenely high priced transformers that yield horrible over-voltage problems. I started using their iron about 20 years ago, before they started their aggressive marketing campaigns. I've been through dozens of units, and I can't tell you how many times I've seen their tweed PT produce heater voltages >= 7.16 VAC. That's really, really BAD.

It's important to know whether a company that is offering repro iron is just doing brain-dead cloning or if they are making adjustments to compensate for increasing line voltages. Mercury had their head pretty far up their ass about this when I started working with them -- their Axiom and ToneClone lines of transformers produced absolutely horrible results. Voltages were out of spec across the board -- including critical heater voltages -- because they turned a blind eye to the voltage problem while they sold "clone" transformers to gullible people who wanted replacement tweed bassman power supply trannies and didn't know any better. I went through dozens of transformers and consistently had the same problem. I spent countless time on the phone with Paul and Sergio trying to address the voltage problems, and they turned a totally deaf ear. It wasn't until a few of us builders started slamming them publicly that their products had such a bad reputation for overvoltage and heater failure that they finally acknowledged the problem with their Axiom and ToneClone lines. They finally introduced the "Plus+" line with primary voltage correction to try to save their reputation from total self-destruction.

I don't have a problem with Terry's gripe about ClassicTone transformers producing over-voltage conditions. Actually, I applaud people who bring this inforamtion to light -- I only wish that he provided a more complete data set that would allow more objective assessment of his experience.

I had been a Mercury customer for years, but eventually I gave up on them and started shopping elsewhere. It just wasn't cost effective to ship 200 lb of iron back to California when they sent me a shipment of crap. Given the cost of freight today, I'd rather deal with someone closer. For me, it's much better to work with a local supplier if/when I can find one. One thing that I like about CT is that they're close to me, and they're willing to bend over backwards to help you. There is that lingering question though, about whether their PSU iron is underspec'd to the point that it doesn't sag under load and ends up giving you voltages that need to be corrected by other means.

Terry, if you could give more details, I'd like to hear them.

[big_teee]

I emailed CT about their excessive B+.
They basically said that, this is what we make, use them or don't!
I emailed them back, and told them I wouldn't use them, and I would pass on their answer.
I've passed it on.
I'm going to try some other brands.
So to summarize, If you are building a 6v6 amp, I would not use the ClassicTone 40-18016.
IME Its B+ is out of bounds for vintage spec 6v6 tubes.
http://www.classictone.net/40-18016.html
As far as Classic-Tone's Customer Service, I'm not at all impressed!
Buy ClassicTone PTs at your own risk, and expect excessive B+ voltages.
T

[Steve A.]

So can we compile a list here of measured B+ in our own experience with specific amps or builds? It might help visitors decide to buy a ClassicTone amp. I would like to know how high their B+ voltages are...

Steve Ahola

P.S. Terry, the CT you mentioned is spec'd at 330v-0-330v. What did you measure at the PT and at the B+ going to the 6V6's (the Fender BFDR AB763 schematic shows a B+ of 420vdc +/- 20% which would be 336vdc to 504vdc. Yikes! I think that the higher percentages might apply to voltages considerably downstream from the power tube plates...)

[eschertron]

(the Fender BFDR AB763 schematic shows a B+ of 420vdc +/- 20% which would be 336vdc to 504vdc. Yikes! I think that the higher percentages might apply to voltages considerably downstream from the power tube plates...)

I wonder where Fender comes up with the +/-20% for a transformer? manufacturing variances? Add to that a line voltage that today can go in excess of +10% of vintage nominal, and...
Maybe the only examples of golden age amps that still exist are the ones that were significantly BELOW rated secondary voltage from the factory? As line voltage changed, the low outliers 'warmed up' to represent the sound we admire so much today, and the high outliers simply blew up.

[big_teee]

Primary voltage here is 120V AC, on the nose.
My B+ with diodes is 485v with tung sol 6v6 tubes at 18ma.
With a Sovtek 5AR4 rectifier it dropped to 455v at 18-20ma.
I got it down to 435v with 2--200 ohm 10 watt resistors in parallel connected to the Center tap ground fuse.
Or electrically it is 100 ohms at 20 watts to ground.
That is where I'm leaving it.
Hopefully the Tung Sol reissue 6V6 tubes will handle the 435V.
After putting in the 100 ohm resistor, I had to rework my bias circuit.
On the 50v bias, I was using a 4.7k input, and changed it to a 10k input resistor to the bias diode.
So far, all is well now, with my JTM-25 Plexi!
In the future, I'm going to try some Edcor PTs.
They have a variety of secondary voltages, and a variety of secondary current level choices.
Their prices are reasonable enough too.
EDCOR - XPWR Series Tube Power Transformers
T
**Clarification
the 18-20ma is setting the bias current for each 6v6 tube.
Not total B+ amp current.

[eschertron]

Thanks for the link to Edcor, Terry! I have only purchased Hammond PTs and OTs so far. I like the way the edcor website looks, too.

[big_teee]

Not speaking for him, but Chuck H said he used Edcor and liked them.
Maybe he can chime in, on what model he uses on his el84s, what model and what B+ he ends up with.
T