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Old 26th August 2011, 09:19 PM   #1
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Default Problem with high voltage in 5e3 build

Hi
Im building an amp with parts from tubetown and ceriatone.
Im using the PT 290BEX (http://www.hammondmfg.com/pdf/EDB290BEX.pdf)
And the amp is built from this layout:http://ceriatone.com/images/layoutPi...3Ceriatone.jpg

I read a plate voltage between pins 3 and 8 on the powertuubes around 420 volts
The voltage on the center tap of the OT is 480 v dc
Im using a sovtek 5y3gt rectifier tube

The Power transformer has an output that is 10 volts higher than it is supposed to, but still, these voltages are way too high?
Any suggestions where to start?

Best regards kasper
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Old 26th August 2011, 09:33 PM   #2
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Are these voltages measured with the tubes pulled? If so, it sounds about right.
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Last edited by leadbelly; 26th August 2011 at 09:35 PM.
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Old 26th August 2011, 10:03 PM   #3
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Yeah! Did not realize the lack of tubes made that big of a difference. With the tubes in, the plate voltage is about 390 ( still a bit high?)
The 6v6gts are drawing 43 milliamps per tube.
the amp is working, but hums a lot, gets louder when turning up the volume.
Have to go to sleep now, but will improve the heater wiring tomorrow.
I live in Denmark, so I use a powercord with only 2 wires in it! The layout calls for a chassis grounded third wire? Is this a problem? The wall outlets here only takes two plugs.
Thanks
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Old 26th August 2011, 11:17 PM   #4
Minion is offline Minion  Canada
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I would recomend getting a Choke for the PSU ... use it in place of the First R in the CRC in the PSU .... it will drop the Voltage a bit more than the resistor but the CLC will have a greater impact on lowering the Hum than a CRC .....

Where possible with the wiring use tightly twisted pair instead of single wires ....

Good luck
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Old 27th August 2011, 02:34 AM   #5
Trout is offline Trout  United States
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Quote:
Originally Posted by bagudan View Post
Hi
Im building an amp with parts from tubetown and ceriatone.
Im using the PT 290BEX (http://www.hammondmfg.com/pdf/EDB290BEX.pdf)
And the amp is built from this layout:http://ceriatone.com/images/layoutPi...3Ceriatone.jpg

I read a plate voltage between pins 3 and 8 on the powertuubes around 420 volts
The voltage on the center tap of the OT is 480 v dc
Im using a sovtek 5y3gt rectifier tube

The Power transformer has an output that is 10 volts higher than it is supposed to, but still, these voltages are way too high?
Any suggestions where to start?

Best regards kasper

Get rid of the Sovtek 5Y3,
A: its not really a 5Y3
B: It does not have the same voltage drop as a 5Y3

Just a FYI,
JJ makes a 5Y3 that DOES run at correct spec. I have used a dozen of them in various tweed amps and all have been spot on for voltage.
Longevity is still questionable, but I have over 200 hours on a couple now with no issues.
NOS 5Y3's are still plentiful as well and not expensive.

According to the Hammond website, you should really be using the 290AEX or 291AEX which is the correct one for the Tweed Deluxe.


The one you have was made for the Blackface & Silverface Deluxe amps which are fixed bias and slightly higher wattage output.
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Old 27th August 2011, 07:46 AM   #6
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Hi
Thanks for the reply. Have been reading lots of post around the web, and it seems youre right, that the sovtek rectifier is no good in this cirquit. Ill try a nos or a JJ then.
According to the tubetown website, the 290bex should work
Tube-Town Online-Store - TT-Chassis Fender Style 5E3 ch-fe5e3

Its the only transformer that fit the chassis they sell.
Thanks for all the help.
Will post again when wires are twisted tihgter and new parts are installed
-Kasper
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Old 27th August 2011, 11:55 AM   #7
Trout is offline Trout  United States
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Location: Midwest Madman
Quote:
Originally Posted by bagudan View Post
Hi
Thanks for the reply. Have been reading lots of post around the web, and it seems youre right, that the sovtek rectifier is no good in this cirquit. Ill try a nos or a JJ then.
According to the tubetown website, the 290bex should work
Tube-Town Online-Store - TT-Chassis Fender Style 5E3 ch-fe5e3

Its the only transformer that fit the chassis they sell.
Thanks for all the help.
Will post again when wires are twisted tihgter and new parts are installed
-Kasper
Hey, that 290BEX/291BEX should be ok, not 100% vintage era correct, but it will be more like the re-issue version voltages.
Drop me an email and I'll send you a very detailed pdf file on the re-issue.
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Old 2nd September 2011, 08:18 PM   #8
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Hmm.
Just recieved my 5y3gt from tubeampdoctor.de today. Should perform as in the old originals.
My voltages are still a tad high, and the amp hums like crazy. Gets louder when using the volume controls.
Voltage on pin3 of powertube: 392v
Voltage on pin 4 of powertube: 344v
Voltage on pin 8 of powertube: 21v

This is measured with all the tubes in.

Im using this output transformer:

Tube-Town Online-Store - Hammond 1760E Fender OT 125A10B / 022913 UPGRADE Princeton ha1760e

Could this be a problem?
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Old 2nd September 2011, 08:27 PM   #9
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Been reading about virtual centertaps (100 ohm resistors from the heater wires to ground)
Maybe I need to do this when Im using the 290bex?
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Old 2nd September 2011, 10:15 PM   #10
Trout is offline Trout  United States
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Quote:
Originally Posted by bagudan View Post
Been reading about virtual centertaps (100 ohm resistors from the heater wires to ground)
Maybe I need to do this when Im using the 290bex?
I always do, you can go to ground, or often guys tie the center point to the power tube cathode(pin8).

As far as the voltages go, using that PT it will always be a tad higher than standard. It was designed for the Blackface Deluxe (22W).

Last edited by Trout; 2nd September 2011 at 10:24 PM.
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