Vox AC30 build pt

Vox and Hiwatt Discussion

Moderators: pompeiisneaks, Colossal

Post Reply
User avatar
JoshBernstein
Posts: 289
Joined: Tue Jan 27, 2015 1:31 am
Location: Key Largo, FL USA

Vox AC30 build pt

Post by JoshBernstein »

Hi there,
I've started to build an ac30, and I've got a power transformer that id like to use, but I'm not 100% sure that it will be sufficient. Its secondaries are as follows: 280-0-280 @ 250ma, 6.3v @ 5 amps, and 5v @ 3 amps. I know the voltages will be fine, but will 250ma be enough on the 280-0-280?
Thanks!
-Josh
Not really
Stevem
Posts: 4551
Joined: Fri Jan 24, 2014 3:01 pm
Location: 1/3rd the way out one of the arms of the Milkyway.

Mmm

Post by Stevem »

Yes that's plenty , you only need 166 ma to power six ax7s and four 84s or 6V6s so your power will be real nice and your Bass will be very tight if that's what your after!
The only this is your V+ voltage will be higher than since the amp is not using all that current at idle .
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: Vox AC30 build pt

Post by martin manning »

I think you'll be fine. Compare the specs for this AC30 replacement PT: http://www.classictone.net/40-18050.pdf
User avatar
JoshBernstein
Posts: 289
Joined: Tue Jan 27, 2015 1:31 am
Location: Key Largo, FL USA

Re: Vox AC30 build pt

Post by JoshBernstein »

Okay cool, thanks. Now about the ot... Looking at the drop-in-replacement specs, the primary for the ot is supposed to be 3.9k. What would be the consequences of using one with a 4.3k primary? How about a 3.8k primary?
Thanks again!
Not really
Stevem
Posts: 4551
Joined: Fri Jan 24, 2014 3:01 pm
Location: 1/3rd the way out one of the arms of the Milkyway.

Bbb

Post by Stevem »

The higher you go in primary impedance the less power output you will have , the longer the output tubes will last, and you will in turn have a lesser amount of output stage distortion .

In short if you want it to sound and respond like a Vox then stick with the stock spec!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
SpeedRacer
Posts: 3
Joined: Fri Jan 09, 2015 6:36 pm
Location: USA

Transformers for AC30

Post by SpeedRacer »

FWIW

- Heyboer has a custom part # I spec'd for them which mounts in the L-style original chassis. You could add an endbell and mount it normally too. It's #8047 I've gigged & recorded with it for about 10 years now. It's solid. It puts 330V on the plates (so 320 across the tube) just like the Mullard specs say to. It is rated for 250mA on the B+ winding. The idea here being to run cool and not melt like the stockers. ;)

- Stock OT is around 4k and is very nicely wound. The older ones used interleaved grain oriented laminations. By the mid 60's they were regular cores (and sounded great too) The OT is one of the keys to the whole amp IMHO. The HF response is dramatically better than any other guitar amp I've spent time with.
pdf64
Posts: 2688
Joined: Sat Mar 12, 2011 9:23 pm
Location: Staffordshire, UK

Re: Transformers for AC30

Post by pdf64 »

SpeedRacer wrote: Heyboer has a custom part # I spec'd for them which mounts in the L-style original chassis. You could add an endbell and mount it normally too. It's #8047 I've gigged & recorded with it for about 10 years now. It's solid. It puts 330V on the plates (so 320 across the tube) just like the Mullard specs say to. It is rated for 250mA on the B+ winding. The idea here being to run cool and not melt like the stockers. ;)...
What's the plate supply impedance of its HT winding?
My understanding is that the PTs intended for tube rectifiers would normally have incorporated sufficient winding impedance to avoid the need for additional resistors. That would naturally result in them running hotter under load than PTs designed without that constraint.
http://www.mif.pg.gda.pl/homepages/fran ... 5/5AR4.pdf
Post Reply