350-0-350 PT w/ EL34s?

[Madison]

Diode driven.
490V on the plates, can they handle it?
I don't want to buy extra caps so does the old +/- 20% rule apply here too?

I can get a 290-0-290 PT.With el34s it's loud but not plexi loud.

Looking to build a 5E3 -50 watt or a 5E5-A or ?

[DummyLoad]

ouch! i wouldn't - near 500V on a 9-pin? will things arc is the question. never mind 100V over 7189A ratings.
DC surge on 500V cap is typically 50V may be OK but cold start B+ may exceed 550V briefly. measure on start up, if on cold start B+ > 550V, then stack caps.

--DL

[jjasilli]

Something is amiss:  el-34's OR el-84's?

[Madison]

EL34s 8 pin.
I did happen to find a 320-0-320 PT also.
Just wondering how far I can push it.

[kagliostro]

Old EL34 can afford 800v B+ (200W from a quartet)

http://www.chambonino.com/construct/const7.html

nowadays the construction isn't so strong

but sure you can use safely the transformer you have

if I'm not wrong the 200W Hiwatt amp (6 x EL34 tubes) uses 650v B+

K

[stratele52]

Marshall put more than 500 volts on their EL34

[phsyconoodler]

Not really.The loaded voltage of most plexis is near 500v,around 497v or so.
  EL34's can take that all day long.Just don't bias too hot or they will melt.
Some say the high voltage plexis sound the best.I tend to agree.

[Madison]

>>Some say the high voltage plexis sound the best.I tend to agree.
I had one in that I build 7 years ago in for service.
It's what made me want to build another high voltage amp.
Been awhile.
I forgot how damn loud and good they sound.

Going to go with cathode bias.
About 270R, I think.

Just worried about the filter caps being overloaded?
Typical 450V filter caps will handle it?
Hoping not to series them.

BTW ordered a PT with 290-320-350 taps if this doesn't work out I'll just go with 320v taps.
Would really like to try the 350V taps!

[alerich]

I run Tung Sol EL34B tubes at 640VDC on the plates in my Sovtek MIG60 (screens are about 350 IIRC) and they are happy as clams and have a huge amount of grunt. I have not tried any other brands and don't intend to. I know the Tung Sols can handle the VDC and they sound fabulous.

[jjasilli]

Let's sort this out. The design question is:  Why a 5E amp with EL-34's?

Could be simple as you are overstocked on EL-34's and have a tranny on hand to match.   Or, are you on a tone quest?

EL-34's can operate over a wide voltage range.  The volume difference over 30 - 40 - 50 watts output is pretty small.  Tone might vary with plate voltage & bias point.  To do A/B tests for tone you like, maybe use a variac with with either PT, 320 or 290.  The variac can scale down, or up to 140%.  Then build the power amp to your preferred plate voltage & bias point.

Everyone should have at least one variac.  I have a black one & a gray one.   

[stratele52]

Not really.The loaded voltage of most plexis is near 500v,around 497v or so.
  EL34's can take that all day long.Just don't bias too hot or they will melt.
Some say the high voltage plexis sound the best.I tend to agree.

I have the Marshall voltages charts and for the Marshall 100 watts , EL34 pin 3 ; 530 volts. And I fix some too.

[Madison]

>>Why a 5E amp with EL-34's?

Want a try making a super grinder.
Made a 5E3 variant (pictured) recently and liked the front and so much thought it would be fun to beef it up.

>>Could be simple as you are overstocked on EL-34's and have a tranny on hand to match.   Or, are you on a tone quest?

Could be.....mostly a tone thang.

>>EL-34's can operate over a wide voltage range.

Will have VVR on board.

[jjasilli]

Will have VVR on board.  Then I'd say go with the high voltage for the power amp.  (Great looking build!)

[DummyLoad]

ouch! i wouldn't - near 500V on a 9-pin? will things arc is the question. never mind 100V over 7189A ratings.
DC surge on 500V cap is typically 50V may be OK but cold start B+ may exceed 550V briefly. measure on start up, if on cold start B+ > 550V, then stack caps.

--DL

sorry for the confusion... major brain fart!  had el84s on my mind i guess...

el34 should have no problems w/ 500V. i have a rauland-borg that claims 75W with 700V to plates. it has two secondaries for B+, and two rectifiers, one each for the plate & screen power supplies. it used a concertina for the PI.

will new prod. el34 take 500V and perform well and reliably? roll the dice...

--DL

[jojokeo]

A 350V tranny will give you loaded ~443Vdc is my "edumacated guess"!? The ol' multiply by 1.41 rarely ever turns out to the actual loaded B+
I'm planning a build currently using a 375V tranny for this reason as I'm looking for ~475Vdc B+ to get those el34 tubes to crunch properly.