EL34 based amps ...... PT Questions

[dreric]

Hey

I know that a quad of el34 and 3 12ax7 need 6.9 ma for the heaters while a quad of 6l6 plus the 3 12ax7 need 4.5 ma.

Are the EL34 based amps like the Blues master and "183" using marshal style PTs? or are they still using twin specs?

They layout Tony did (thank you) show the old Magic Parts TL 130. I know they no longer sell the brand that HAD used and I can't find specs on them.

With the EL34 do I use a different choke.

Thanks

Eric

[Structo]

Eric,
My data shows that EL34's draw 1.5 amps heater current per tube.

4 x 1.5 = 6 amps

12ax7's draw .3 amps each for a total of .9 or 1 amp for three tubes.

So that is a total of 7 amps just for the heaters.

I don't know for sure but I would assume that those amps used Marshall style transformers because of the load and output.

[bigmik]

I'm not sure if HAD used marshall PT's in some if his builds but 183 used a fender twin reverb replacement from magic parts TF_130 which is desinged for 6l6's yet is used to run el34's .

maybe it's a beefed up version? does anybody know?

http://www.magicparts.com/new/default.htm

Eric,

My data shows that EL34's draw 1.5 amps heater current per tube.

4 x 1.5 = 6 amps

12ax7's draw .3 amps each for a total of .9 or 1 amp for three tubes.

So that is a total of 7 amps just for the heaters.

I don't know for sure but I would assume that those amps used Marshall style transformers because of the load and output.

[dreric]

The 183 thread prompted this question. To quote "phoenix" from that thread:

TMI manufactured the “TF” series of transformers for Magic Parts up until 2002/03. If you order the TF series from Magic Parts today, you’ll not get the same iron HAD used. More likely Marvel Electric Corp. (EIA code 989).

TF-130 is Magic Part's part number.

So seeing that the original may not be readily available I started to wonder if there are differences in the PT for the EL 34 based amps.

For a Marshall style transformer:

http://classictone.net/40-18046.pdf

Which has the heater ma but also higher secondaries (700 volts if I read the specs right) versus the Twin iron:

http://classictone.net/40-18004.pdf

With 420V on the secondaries.

I'm not clear on whether HAD used twin PT for his EL34 based amps stressing the heaters and having less on the plates or if he used Marshall PT for these amps.

And regardless of what HAD did what are the guys who have completed EL34 based amps using???

Thanks

Eric

[Structo]

Eric, I used the Magnetic Components Twin set of transformers and choke in my latest build.

I am getting 433v on the plates. That's at 120 vac wall voltage.
If you recall my build I used the older style power supply and filtering so I'm not positive if the voltages are the same with the precision supply.


What I don't like about the Twin PT is that the heater voltage is a bit high.
They spec it at 6.5v for some reason but I get 6.7v measured.


The problem with that Marshall PT is that it doesn't have a bias tap so you would have to take the bias voltage from the HT.
That is also the export version, which you may or may not like.

[67plexi]

Magnetic Components Power transformer twin.
I used a set and had low output on B+ 420vac
Replaced the power transformer with a new MC 465vac B+
great second transformer WTF is up with that ?


Steve.

[bigmik]

on my el34 HRM i built some time ago I used mag comp jcm 800 replacement power and output trannys ,ended up with about 470 V on the
plates. good iron.

[ToneMerc]

And regardless of what HAD did what are the guys who have completed EL34 based amps using???
Eric

For any Twin style PT, I usually have Heyboer wind an one with an extra 6.3V/750mA tap and 8A on the filaments.

TM

[jborders5]

FYI, I'm ordering a small run of Heyboer upgraded twin style power transformers next week that will handle EL34s. https://tubeamparchive.com/viewtopic.php?t=12900 . Let me know if you want to be added to the list.

[Structo]

Magnetic Components Power transformer twin.
I used a set and had low output on B+ 420vac
Replaced the power transformer with a new MC 465vac B+
great second transformer WTF is up with that ?


Steve.

Steve did you return the MC PT?

My voltage is lower than I thought it should be at 433v
Fender Twin schematics show 450-460v on the plates.

[TheHandsomeOrk]

My voltage is lower than I thought it should be at 433v
Fender Twin schematics show 450-460v on the plates.[/quote]

I'm always surprised when using Twin PT as I expect higher voltages.
Built 3 so far ( I'm a hobbyist not a build for profit guy) with similar results
using different caps ( rules that out) and different brand transformers including a mercury magnets, always the same result. I expect to see 450-460v according to the math but end up with 430-435. Must be the loss in the trannys themselves. Built a 50w using a Fender blues deville PT which gave 488v on the plates another surprise.
I know that mercury magnets and formica boards = bland sounding amp.

[67plexi]

Tom. I still have the low voltage under load transformer MC.
I built a new amp MC power, 1970 twin choke, 1970 twin output 465v plate.
The second amp is what dreams are made of it kick's sonic butt.
May be the MC power transformer,choke,output I don't know.
I will not use MC from now on. I don't have a shunt to test the transformer under load. but it is ok on all other test but not under load.

Steve.

[Structo]

Do you think that you get better tone with the higher voltage?

I was told that my tubes will last longer and that the voltage I have is fine.

[ToneMerc]

FYI, I'm ordering a small run of Heyboer upgraded twin style power transformers next week that will handle EL34s. https://tubeamparchive.com/viewtopic.php?t=12900 . Let me know if you want to be added to the list.

Jason, I might be interested if the HT voltage and current specs are a tad higher than the stock trans.

TM

[jborders5]

FYI, I'm ordering a small run of Heyboer upgraded twin style power transformers next week that will handle EL34s. https://tubeamparchive.com/viewtopic.php?t=12900 . Let me know if you want to be added to the list.

Jason, I might be interested if the HT voltage and current specs are a tad higher than the stock trans.

TM

These are the initial specs the quote was based on. I should have the shop drawings for approval on Monday or Tuesday.

[img:448:483]http://img717.imageshack.us/img717/213/powerxformer.jpg[/img]