FDP Home Page / FDP Forum / FAQ's

The FDP is made possible by the following companies and individual members like you.
Please use the links below to show them we value their sponsorship.

Jensen Loudspeakers

Sweetwater

Amplified Parts

Apex Tube Matching

WD Music

MOD KITS DIY

Yellowjackets Tube Converters

Antique Electronics Supply


* God bless America and our men and women in uniform *

* Illegitimi non carborundum! *

If you benefit and learn from the FDP and enjoy our site, please help support us and become a Contributing Member or make a Donation today! The FDP counts on YOU to help keep the site going with an annual contribution. It's quick and easy with PayPal. Please do it TODAY!

Chris Greene, Host & Founder

LOST YOUR PASSWORD?

......................................................................

   
FDP Jam
Calendar
Find musicians
in your area!
  Search the Forums  

FDP Forum / Amp Mods, Repairs, and Projects / hammond 290CAX Power trans heater voltage question

grsmnkey
Contributing Member

USA/NH

Jan 31st, 2019 01:01 PM   Edit   Profile  

I recently built a 6G2 Princeton clone and have a power transformer question.

I ended up ordering a Classic Tone 40-18019 transformer. While the spec sheet shows at 120V it should have 6.3V for the heaters, I am getting 7.2 at about 122V.

Does anyone have any experience using the Hammond 290CAX? The spec sheet also shows 6.3V @ 120V.

I am not too concerned with plate voltage. I want to loan the amp out to my nephew without running a Variac or other voltage reducing device. I did check around the, but most people are looking at plate voltage and don't really mention the heater voltage.



Elmo66
Contributing Member
**********
**

Midwest USA

Jan 31st, 2019 07:24 PM   Edit   Profile  

You'll be fine. 1 volt ain't gonna kill anything.

Peegoo
Contributing Member
**********
**********
**********
****

Just beyond Mars

there's a world of fools
Feb 8th, 2019 02:02 PM   Edit   Profile  

Yeah, not a problem, considering it's running all the tube heater filaments and the power jewel lamp. Better to have 7v than 5v.

pdf64

UK

Feb 10th, 2019 04:47 AM   Edit   Profile  

I think it's a problem, voltage 14% above nominal means that the tube heater power will be ~30% greater than intended (power = voltage squared over resistance).
The limiting value for heater voltage is usually 10% (6.9V), though I've seen it as low as 5% (6.6V).
And bear in mind that USA mains voltage can be even higher, even 129 for limited times.
It's unfortunate that PTs so inappropriate for modern North American mains voltages are being made.
I suggest that series dropping resistor/s are used, eg metal cased, bolted to the chassis, with thermal grease.

Regarding tube heaters, their failure modes and mitigation, see Tomer p11-18 http://www.tubebooks.org/Books/Atwood/Tomer%201960%20Getting%20the%20Most%20Out%20of%20Vacuum%20Tubes.pdf
Merlin also mentions the topic http://www.valvewizard.co.uk/heater.html

(This message was last edited by pdf64 at 11:14 AM, Feb 12th, 2019)

grsmnkey
Contributing Member

USA/NH

Feb 10th, 2019 09:30 AM   Edit   Profile  

Thanks for the replies.

I couldn't find any outside confirmation about the Hammond PT so I did what pdf64 suggested and used some dropping resistors for the heater circuit.

I did blow out the heater on an NOS 12ax7, which started me on this quest. I also have found that new production tubes seem to withstand the strain.

At 7.2V the heaters are very bright, now they are at 6.4 and everything is much better. It seems to sound less aggressive when pushed, though that's probably just my imagination.

I'm still thinking about the Hammond for the future if there are problems with plate voltage.

Elmo66
Contributing Member
**********
**

Midwest USA

Feb 10th, 2019 08:27 PM   Edit   Profile  

Are you measuring that 7.2 volts under load with the tubes in place, or strictly off the transformer with no tubes?

grsmnkey
Contributing Member

USA/NH

Feb 11th, 2019 08:15 AM   Edit   Profile  

Under load. When I used it, I ran it through an Amp Maniac at 109V to get the heaters down. So it's definitely the PT. Problem is resolved for lending it out.

Plate voltage is a bit high, but the same in comparing to other's results. If I choose, sometime in the future, I may buy the Hammond PT and remove dropping resisters I added for the heaters.

pdf64

UK

Feb 12th, 2019 03:25 AM   Edit   Profile  

I would contact Classictone, as on the face of it, the PT seems to have a winding ratio error.

Leftee
Contributing Member
**********
**********
**********
**********

VA

Toxic Humility
Feb 12th, 2019 04:58 AM   Edit   Profile  

Winding ratio or the location of taps?

grsmnkey
Contributing Member

USA/NH

Feb 12th, 2019 07:14 AM   Edit   Profile  

I don't want anyone to get the idea that all ClassicTone PT have the same problem.

I did purchase another PT from them for a Brown Bandmaster and the voltages were close to exact specifications using 120V from the wall.

I'm willing to bet that the 40-18019 has always been this way. Doing a bit of research, all my other voltages are as others have reported for this PT. It's just hardly anyone posts the Heater voltage.

FDP Forum / Amp Mods, Repairs, and Projects / hammond 290CAX Power trans heater voltage question




Reply to this Topic
Display my email address             Lost your password?
Your Message:
Link Address (URL):
Link Title:




Moderators: Chris Greene  Iron Man  reverendrob  

FDP, LLC Privacy Policy: Your real name, username, and email
are held in confidence and not disclosed to any third parties, sold, or
used for anything other than FDP Forum registration unless you specifically authorize disclosure.

Furtkamp.com 
Internet Application Development

Copyright © 1999-2019 Fender Discussion Page, LLC   All Rights Reserved