Problem with high voltage in 5e3 build

[bagudan]

Hi
I´m building an amp with parts from tubetown and ceriatone.
I´m using the PT 290BEX (http://www.hammondmfg.com/pdf/EDB290BEX.pdf)
And the amp is built from this layout:http://ceriatone.com/images/layoutPic/fenderLayout/5E3Ceriatone.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
I´m 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

 

[leadbelly]

Are these voltages measured with the tubes pulled? If so, it sounds about right.

 

[bagudan]

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 6v6gt´s 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

 

[Minion]

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

 

[Trout]

Hi
I´m building an amp with parts from tubetown and ceriatone.
I´m using the PT 290BEX (http://www.hammondmfg.com/pdf/EDB290BEX.pdf)
And the amp is built from this layout:http://ceriatone.com/images/layoutPic/fenderLayout/5E3Ceriatone.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
I´m 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.

 

[bagudan]

Hi
Thanks for the reply. Have been reading lots of post around the web, and it seems you´re right, that the sovtek rectifier is no good in this cirquit. I´ll 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

It´s 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

 

[Trout]

Hi
Thanks for the reply. Have been reading lots of post around the web, and it seems you´re right, that the sovtek rectifier is no good in this cirquit. I´ll 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

It´s 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.

 

[bagudan]

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.

I´m using this output transformer:

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

Could this be a problem?

 

[bagudan]

Been reading about virtual centertaps (100 ohm resistors from the heater wires to ground)
Maybe I need to do this when I´m using the 290bex?

 

[Trout]

Been reading about virtual centertaps (100 ohm resistors from the heater wires to ground)
Maybe I need to do this when I´m 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).

 

[bagudan]

Thanks man.
My power supply does not have a center tap for the heaters, so maybe this is causing the hum?

 

[Nigel Goodwin]

Thanks man.
My power supply does not have a center tap for the heaters, so maybe this is causing the hum?

Are you using twisted pairs for the heaters?, and carefully routing them?.

If your transformer isn't center tapped, then it used to common to have a preset resistor connected across the heater feed, with the slider to chassis - you then adjust it for minimum hum.

The 'posh' version of what you mentioned.

 

[bagudan]

Thanks
Just making sure I get it right.

Would a 4 watt 220r potentiometer, with the outer lugs connected to the two heaters, and the middle lug connected to ground work?

-Kasper

 

[Trout]

Thanks
Just making sure I get it right.

Would a 4 watt 220r potentiometer, with the outer lugs connected to the two heaters, and the middle lug connected to ground work?

-Kasper

Yes, that will work just fine but honestly, on a 5E3 (and I have built a lot of them) the pot route is not mandatory. You will be just fine using 2- 100R resistors.

Look at the factory drawings I sent you on the 5E3 re-issue, if you set it up like that it will be just fine.

95% of the time if you are getting hum in a 5E3 with the artificial CT resistors the problem is generally poor grounding practices or lead dress.

 

[bagudan]

Ok thanks again
will try with the two resistors then.

it´ll be several days again waiting for parts to arrive.... hate that<1

Will let you know how it turns out

-Kasper

 

[Nigel Goodwin]

Thanks
Just making sure I get it right.

Would a 4 watt 220r potentiometer, with the outer lugs connected to the two heaters, and the middle lug connected to ground work?

Yes, the advantage is it's adjustable - but it's mostly a concern for high gain devices such as tape recorders.

 

[bagudan]

Well. Resistors are ordered. while waiting I´m trying to find out if other things in my build could cause hum.
Some guys on the web use input and speaker jacks that are isolated from the chassis. Have also seen examples of pots isolated fro chassis.

Both my pots and jacks are all touching chassis. Is this also a problem?

Maybe I should have taken the more expensive route and bought a kit 😉
But guess I´m learning things this way?

 

[Nigel Goodwin]

Can you post a picture of your build?.

 

[bagudan]

Of course!
Some of the images give an impression of twice the amount of wires... It´s just a mirrorshiny enclosure!

Not too proud of the wiring at the input jacks😉

If it´s bad... seriously! Then let me have it. I can take it, and want to learn.
Aprreciate the help from you guys!

 

[Nigel Goodwin]

That doesn't look too bad 😀

Have you isolated where the hum is coming from?, do the volume controls affect it's level?, and how does removing each of the triodes affect it?.