Beginner with MM 5e3 PT question

[budswallers]

Hi, I am about to attempt my first amp build. I decided to go with a tweed deluxe. Money is tight and I have had to scrounge for parts and pinch pennies where I could to aquire quality components.

I purchased a MM PT via ebay, and had assumed they would all be pretty similar. This model is a( FTDP-M Tweed -- lowest B+ -- 290-0-290 unloaded ). These numbers look quite a bit lower than others I have seen. My question is how will this affect my amp? I will be following a basic fender schematic (nothing changed but 3 prong power cord and standby switch). Are there any values of components I should change to make up for a low b+ and lower voltage (I have seen many ideal values most seem to be around 320-340, I am confused on that issue).

I was about all ready to solder this up but began to wonder if the difference in my PT would affect the values of compontents used. No reason to solder in stock values if they would not be correct to optimize this PT and get the best sound from the tubes.

I kindly thank you for any help you may provide.

[tubeswell]

the classic 5E3 used 325-0-325@70mA, 6.3V @ 2A, 5V @2A, and it got its ~350-360 B+ ballpark with a 5Y3GT and 16uF reservoir.

However altho' 290 is a bit lower, you can use a 5R4 or 5V4 to get more juice on the B+. A GZ34 would get the B+ to around 380 (with say 40-60uF reservoir), but it will be cleaner and tighter than a vintage 5e3, which you may or may not like. 2CW

[budswallers]

Thank you for the reply tubeswell. I am still painting by numbers on this build so to speak and do not quite yet see how one thing influences another. So if I would just build this to stock spec with this PT the amp would sound terrible? I was hoping it would just be quieter/less watts. Lot to learn.

When you say resivoir...do you mean the large capacitors that are 16uf in the stock scheme(replace them with 40-60uf caps and the rectifier you mention)? That would bring it close to stock specs?

Thanks very much for the info. I would hate to have to purchase another PT so any help I can get to make this one into an okay sounding 5e3 would be greatly appreciated. I will just have to make due and upgrade to the correct PT in the future.

[tubeswell]

You can build it with that PT and adjust the bias voltage to get a higher idle current if the plate voltage is lower. It will sound 'thicker' this way. If you don't like it you can always get another PT later.

The reservoir cap is the first filter cap after the rectifier. It functions to substantially fill up the 'troughs' between the pulses of charge from the rectifier, so that the HT voltage starts to resemble something of a continuous DC voltage for the B+ supply. Rectifier tube datasheets will specify a maximum capacitance for the reservoir cap - to ensure that the tube has a reasonable life expectancy. The higher the capacitance of the reservoir, the harder it is on the tube, but the cleaner it sounds, up to a point.

[tyru007]

Using Duncans PSU designer, the 290-0-290 PT with a 5y3 rectifier is going to give you a low voltage. Plate - Screen and Preamp tap voltages of about 315, 270 and 190V.

You might try a GZ34/5AR4 rectifier with an additional 100R to 150R wirewound 10watt or 25 watt power resistor between the rectifier and the first plate tap to add back some power "sag" that the 5Y3 would normally give you.

http://www.mouser.com/ProductDetail/...59BHTCWj1ms%3d

Voltages would then be around 360 (plate tap), 310 (screen tap) and 225 (preamp tap).

This would also be a nice PT for a Champ or Princeton 5F2-A amp, however, you would need a single ended output transformer instead of a Push-Pull OT.

[Philr228]

You could also try a Sovtek 5y3 they are good and cheap (it's not really a 5Y3) it should give you the right voltages too, I used one in my 5E3 build using a Hammond 300-0-300 100mA PT and I've got 370Vdc of B+. Just remember that should you or anyone replace it at a later date that a different 5Y3 will give you different voltages.

[budswallers]

Thank you

Thank you all for taking the time to reply. These answers are very helpful to me. Seems there are so many possibilities.

Philr- Seems you used a similar tranny. You used all stock values for caps and resistors and got correct voltages with the sovtek? That is good to hear! I am curious as to what you used for your cathode bias resistor(i believe that is what it is) the large 250 ohm 5 watt one.

Where you happy with the sound of the amp? Do you know what kind of output you ended up with in watts? Hope that is not too many questions.

Cheers

[Philr228]

Bud,

Sorry for the delayed reply not looked here for a while!

I used all stock parts, as close as I could easily access anyway, 22uF filter caps., 22uF 25V cathode caps. and a 253 Ohm cathode resistor (a 200 Ohm and a 33 Ohm 5 watt resistors in series). I used a Hammond 125E output transformer too, sounds beautiful.

All this gave a power dissipation of 13.4 watts thereabouts and bias current of around 39mA. I'm going to try a 270 Ohm resistor to see if it will lower dissipation and bias current slightly and extend the life of my 6V6EH's.

See my thread (http://music-electronics-forum.com/t15558/) for my calculations and voltages. Hope it all helps.

Phil