Quick question - installing new Power Transformer.

[Stratz]

Hi All.
Because of high B+ on my Deluxe Reverb build I'm trying my Classic Tone 40-1806 in place of the Mojo/Heyboer 761.

I’m stuck installing the new Classic Tone PT. It has a blue wire which says BIAS on the Classic Tone schematic. The Heyboer has a red/blue wire going to the 470 ohm resistor on the bias board.

The Mojo/Heyboer 761 also has 2 black wires. One goes to the outside of the fuse holder and the other goes to the power switch. I’m guessing the white wire goes to the power switch or it simply doesn’t matter.

Thanks again all.
Rob.

[g1]

That classic tone link is for an output transformer.

[Tom Phillips]

...The Mojo/Heyboer 761 also has 2 black wires. One goes to the outside of the fuse holder and the other goes to the power switch. I’m guessing the white wire goes to the power switch or it simply doesn’t matter...

That describes the old method of wiring a two wire line cord where the fuse is in one leg of the power line input and the switch is in the other. The switch and the fuse are both placed in series in the hot lead per modern wiring code for a three wire (grounded) system. The modern method should be used for new builds and for grounded power cord upgrades on old equipment. You can see examples of the modern method by checking out new schematics and the schematics for the re-issue amps. You will find other discussions covering this subject on MEF such as the one at http://music-electronics-forum.com/t35916/

[Stratz]

Sorry about that G. I figured it out. It was a pretty dumb question in retrospect.
Thanks for taking a look though.
Rob.

[Stratz]

Thanks Tom.
As for the blue bias wire. I thought the Classict Tone PT had both the red/blue and blue but there was only blue so it was evident where it went.

For anyone interested. The Classic Tone 40-18016 PT states 330-0-330 while the Mojo 761 states 362-362.

I measured 448 volts at the plates @19mA with the higher rated Mojo 761.

With the lower rated CT 40-18016 I now have 453 v at the plates @19ma
Line voltage was the same (119-120v) when measuring both.

[Tom Phillips]

...The Classic Tone 40-18016 PT states 330-0-330 while the Mojo 761 states 362-362.

I measured 448 volts at the plates @19mA with the higher rated Mojo 761.

With the lower rated CT 40-18016 I now have 453 v at the plates @19ma
Line voltage was the same (119-120v) when measuring both.

So you say that the B+ went up when the secondary voltage went down? There's a typo in there somewhere. Correct?

[Stratz]

So you say that the B+ went up when the secondary voltage went down? There's a typo in there somewhere. Correct?

There are no typo's Tom. The measurements stated are correct. The readings were taken from my bias tool. Perhaps it's giving me incorrect readings.

The 6V6 pin 3 plate voltage of the Classic Tone PT measures 436v with my DMM. I dont have these measurements from the original Mojo 761 PT. Sorry.

I'm new to amp building Tom so could you kindly explain what secondary voltage means?
Thank you
Rob.

[big_teee]

Those are the same voltages I had with the CT 40-18016 PT.
http://www.classictone.net/40-18016.pdf
I have 455V with the 19ma using a 5AR4 Rectifier tube.
That is why I'm not going to buy anymore Classic Tone PTs.
3 amp builds and all with higher voltages than specs.
T

[g1]

There are no typo's Tom. The measurements stated are correct. The readings were taken from my bias tool. Perhaps it's giving me incorrect readings.

Then perhaps the typo is in the literature for one of those PT's.
The only way to tell for sure would be to load the secondaries as specified and measure the secondary voltage.

[big_teee]

Since these 120ma PTs are primarily used for 6V6s?
I wonder why they don't make them for 6V6 Maximum Specs?
All voltages are within limits, except for the B+, which is way too high.
Especially if you use any vintage type tubes.
T
** I emailed CT about their High B+ on some of their PTs.
I wll let you know what their response is.

[potatofarmer]

It occurs to me - least intelligent guy in the room here! - that ClassicTone specifies that transformer as "330-0-330 @120 mA", which tells us nothing about its unloaded (or idle) voltages. They don't even provide a regulation percentage, so I suspect CT will just tell you that it's performing exactly as advertised.

[big_teee]

It occurs to me - least intelligent guy in the room here! - that ClassicTone specifies that transformer as "330-0-330 @120 mA", which tells us nothing about its unloaded (or idle) voltages. They don't even provide a regulation percentage, so I suspect CT will just tell you that it's performing exactly as advertised.

You're correct, and ClassicTone could care less!
The problem with that, is the amps they recommend this PT for doesn't load the circuit enough to drop the voltage from 455v with a 5AR4.
I will try other brand and other voltage PTs in the future.
Anyone building a 6V6 amp using vintage type tubes, I wouldn't use the CT 40-18016 PT.
That is strictly my own experience, and YMMV.
GL
T

[valvetrain]

You're correct, and ClassicTone could care less!
The problem with that, is the amps they recommend this PT for doesn't load the circuit enough to drop the voltage from 455v with a 5AR4.
I will try other brand and other voltage PTs in the future.
Anyone building a 6V6 amp using vintage type tubes, I wouldn't use the CT 40-18016 PT.
That is strictly my own experience, and YMMV.
GL
T

OK folks, I've watched this thread with obvious interest...
I have use these parts for years and have sold a TON of them...

So... IMHO it's time to get off the soapboxes and wait while i get on mine and then please listen to what I have to say about these transformers...
#1... ClassicTone does care (as do I... Rick Gessner techsupport@amppartsdirect.com)
#2... The ClassicTone Transformers are rated at the FULLY LOADED voltage, not unloaded or idle voltage...
#3... The ClassicTone 40-18016 units normally run about 20vDC less at the plates than the Heyboer/Mojo units...
#4... Transformers are rated at +/- 5% and always have been...
#5... The vintage Fender schematics were traditionally rated at 117vAC of input.
#6... Vintage rectifiers (RCA, Mullard, etc) do not produce as much voltage as the current production units. (JJ, Sovtek)

I have an early 1964 DR on the bench as we speak (or write as the case may be) with a Schumacher PT dated 313...
With 120vAC on the input, the unloaded voltage at the red leads is 343.6vAC... a brand new 40-18016 is hitting 349.2... (about a 1.6% variance)
so there is negligible difference given the age of the original Fender unit... (compared to the 362 rating of the Mojo/Heyboer unit)
The original amp pulls the circuit down to about 418 at the plates and 420 at the first filter cap. so i would not expect much different behavior
from the 40-18016.

so... please.... before you wield your weapons and start speaking for other folks (like how ClassicTone doesn't care)
PLEASE verify your data... and check your tubes, make sure your meter is accurate and has fresh batteries...

Then... if the 40-18016 is still too high for you application, please consider the 40-18028 which has a second set of secondary taps that are 10%
lower voltage than the main set just to bring the B+ down to where you might find it more comfortable...

{PLOP} sorry... fell off my soapbox...

At any rate, please don't throw unsubstantiated rocks...
these parts are for the most part deadly accurate and we do our best to offer alternatives that try to address
the personal preferences in the design and implementation of vintage style tube amps...

Again, all of this is just IMHO, but remember, please don't flame me out too bad, because i am the guy that will end up trying to answer most of your questions anyway...

Rick

[big_teee]

Hi Rick:
No flaming anyone.
I just call things as I see them.
BTW, I bought the 6v6 iron set from your company.
I didn't contact you about my voltage problem, but went direct to ClassicTone.
I love the CT OTs and Chokes.
But, for now I'm done with their PTs.
3 different amp builds, and all 3 with very high HT B+.
I reserve the right to come back to CT PTs, but most likely for future builds, I'm Thinking of doing something else.
T

[valvetrain]

Hi Rick:
No flaming anyone.
I just call things as I see them.
BTW, I bought the 6v6 iron set from your company.
I didn't contact you about my voltage problem, but went direct to ClassicTone.
I love the CT OTs and Chokes.
But, for now I'm done with their PTs.
3 different amp builds, and all 3 with very high HT B+.
I reserve the right to come back to CT PTs, but most likely for future builds, I'm Thinking of doing something else.
T

Just curious, Are all 3 of these builds 100% clones of the original circuits or are they modified in some way?
Trying to rationalize why you are seeing a variance and i traditionally don't see that much deviation...