Metropoulos Forum

Hello guys I need your help.
I'm starting to build a new 50W 1987 and I ask you about anodic tension

On my secondary PT I have two anodic Output : 325V or 350V.
I'm wondering which is better voltage value for this model. I'm following the http://home.comcast.net/~jbjdav26/1987r17.jpg" onclick="window.open(this.href);return false; layout with main and screen caps 50u + 50u

Thanks
Massimo

For a 50w rectifier:

Vdc=2 Vmax/pi = 0.637 Vmax

so 325v = 650 x 0.637 = Approx 414v dc

350v = 700 x 0.637 = 445.9v dc

My 67 and 68 50 watters with 1202-118 PT both put about 420v on the plates of the EL34s depending on where the bias is set.

Higher voltage will be a bit crisper and lower voltage a bit browner, but not much difference IMO.

Late metal panel 50w had plate voltages as low as 370v which does make them quieter and browner. You can influence the way the preamp behaves by which B+ droppers you use (8k2 between screens and PI followed by 10k and 10k in early amps, or 8k2 + 8k2 and 10k + 10k later) and all variations in between .

What particular tones are you after?

Many Thanks for your reply Neil!

I'd like to have an Rock / Hard Rock oriented tone ... this is my Power Transfer Model :

http://www.ig-transformatoren.com/produ ... 550RL.html" onclick="window.open(this.href);return false;

Thanks Massimo

I'd go low voltage with 50/50 preamp, 50 PI and 50 screens with 100uF mains (ie x3 50/50 cans each rated 500v).

Hello Neil
Do you think 32 + 32 UF on preamp should give a smoother gain?
Many Thanks
Massimo

I personally prefer 32uF in the preamp but was going with your 70s metal/rock theme

neikeel wrote:I personally prefer 32uF in the preamp but was going with your 70s metal/rock theme

This sounds good Neil! I love 70's marshall tone ... My cd playing Thin lizzy now !!
I suppose 32 + 32 should be fit good for me!!

Hi,
for those power supply: arround 430 V dc for 325 v AC ; 465 V dc for 350 v AC ( no load voltage).
Don't use 350 V ac if you use one 500 v anode filter cap.; pp voltage is almost 500 v, it is too much
Catalin

catalin gramada wrote:Hi,
for those power supply: arround 430 V dc for 325 v AC ; 465 V dc for 350 v AC ( no load voltage).
Don't use 350 V ac if you use one 500 v anode filter cap.; pp voltage is almost 500 v, it is too much
Catalin

Ok Thanks for your details