Valve jr tube question

[Devon8822]

Im sure its in the valve jr thread but icannot go through all of those pages. Anyways, this is my first post, glad to join this great forum!

I am wondering someone could tell me (or direct me to the answer). I want use a valve jr for a tube tester for some vintage marshalls. I ened to to take ecc83 (already does) and el34s (doesnt take em) so I want to mod it to take el34s. First of all I want to know how it sounds with el34s instead of el84s? better worse? secondly Im guessing that it will work right?

How do I perform this mod, I would need a step by step instruction for a big amp noob. thanks!

[Mooreamps]

When I did the 18 watt upgrade to my bench chassis, it involved adding an EL34 and a 6L6. I had to add an additional 12 volt power transformer to handle filament power for the power tubes. The stock power transformer can not handle the additional heater load.

-g

[zaphod_phil]

Im sure its in the valve jr thread but icannot go through all of those pages.

A poor excuse I'm afraid. Just start at the last page of the main thread and step back pages until you find what you want, or better still go to the Valve Junior repository thread where the various schematics and mod details are stored. You can also pop your question into the main VJr thread, where all the VJr modding guys will see it.

Yes, you can run an eL34 quite easily in a VJr. The PT does have enough heater current for a single EL34, although you should upgrade the OT to one that can handle more anode current, such as a Hammond 125ESE.

[Devon8822]

mmm ok, what happens if i dont upgrade the transformer, it just wont sound as good?

Does a valve jr sound as ood with an el34 as it does with a el84?

does anyone have the knowledge of the whereabouts of the instructions for this mod? thanks

[zaphod_phil]

If you don't upgrade the transformer, you may well cook it with an EL34. Apart from the amp not sounding as good. IMO an EL34 sounds way better in an SE amp than an EL84. EL34s have a bigger, warmer tone, while EL84s can sound somewhat shrill in an SE amp.

Here's the schematic - http://www.18watt.com/modules.php?name= ... ad&id=6506

It's from this sticky thread - http://www.18watt.com/modules.php?name= ... ic&t=16138

[Devon8822]

Thanks for the schematic mate! I have a couple question please excuse me lack of knowledge in this subject.

What is an SE amp?

So you say el34s will sound better than el84s in a VJ, mmm is this even if i leave the transformer stock? So basically what im asking is will the el34 sound better than an el84 in a VJ without changing the transformer?

If i do decide to change the transformer if cost permits, will the el34 sound better with a transformer that can handle it better?

thanks for you help I hope you can answer my questions.

[Bluesmechanic]

What is an SE amp?

SE is short for "Single Ended". The VJr. is single ended. The technical explanation of why it is single ended can be found all over the Net. Having one power tube does not make it single ended. Are you confused? Me too.

Edit: An amp could have two power tubes and still be single ended. (Like Garys). So having one power tube does and it doesn't make it SE. Did I just say that?

[Mooreamps]

General rule of thumb, if it's a guitar amp, and if it has only one power tube, and if it sounds half way functional, it's a good guess it's a single-ended amp.

In comparision, push-pull amps, like the kind that we are supposed to be talking about on this forum, have power tube pairs driving a push-pull output transformer, some 4 power tube, and still others with 6 power tubes.

The only thing with having more than two power tubes running single ended, or class A, is the amp tends to sound less single ended.

[zaphod_phil]

So you say el34s will sound better than el84s in a VJ, mmm is this even if i leave the transformer stock? So basically what im asking is will the el34 sound better than an el84 in a VJ without changing the transformer? If i do decide to change the transformer if cost permits, will the el34 sound better with a transformer that can handle it better?

The VJr stock OT isn't suitable for an EL34. You need something a lot beefier to handle the EL34's current draw, and provide lower load impedances. Just put in a Hammond 125ESE, and you'll be away. And the good news you can also use other power tubes with that transformer as well.