ST35 voltages WAY too high! - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 11th April 2008, 03:10 AM   #1
diyAudio Member
 
Join Date: Jun 2005
Location: USA
Send a message via AIM to ThSpeakerDude88
Default ST35 voltages WAY too high!

Hey I just got my scratch built ST35 up and running. I've got a PA774 repro power tranny and hammond 1650F's on the outputs.
I am using the stock power supply with 2x1n4007 and a little more capacitance. 100uf-50ohm-100uf-6.8k-22uf.

At the plates, I am reading 440v! My bias voltage is also 16v. I've heard of voltages being a little high in these things, but only on the order of 380v or so. What should I do? Also, the power transformer buzzes pretty nastily.. I'm thinking I might have had less problems with a freakin hammond I even tried tightening up the laminations but it didn't help too much.


There is also an audible buzz through the speakers when it is on...it is definatly power line induced because as soon as you unplug the amp it stops.

Anyways, anyone else find these voltages pretty nasty for an EL84? I understand I could go with 7189's, but I'd prefer to use my quad of mullard's for now..
__________________
always preach the gospel-
and when necessary use words.
  Reply With Quote
Old 11th April 2008, 12:57 PM   #2
diyAudio Member
 
Join Date: Jun 2005
Location: USA
Send a message via AIM to ThSpeakerDude88
Anyone....? I can't seem to find much info about this on the net...
__________________
always preach the gospel-
and when necessary use words.
  Reply With Quote
Old 11th April 2008, 04:22 PM   #3
diyAudio Member
 
Ty_Bower's Avatar
 
Join Date: Mar 2007
Location: Newark, DE
I thought the B+ on my ST-35 clone was high at 410 volts. You can read more about it here:
http://www.diytube.com/phpBB2/viewtopic.php?t=1646

What you are seeing sounds like something is wrong. What is your line (AC) voltage? Where did you get your PA774? Do you have a variac? If the B+ is so high, what is the heater (6.3VAC) voltage doing?
  Reply With Quote
Old 14th April 2008, 12:03 AM   #4
diyAudio Member
 
Join Date: Jun 2005
Location: USA
Send a message via AIM to ThSpeakerDude88
Im pretty sure the heaters are around 7v , a lot of my amps do that if they have low resistance windings ( IE arent loaded easily.) I will measure tonight to see. My line voltage is always around 123-124v which makes working with 117v transformers no fun . I got my pa 774 from triode electronics..its a new transformer and I ASKED AROUND and everyones opinion was that it was redesigned for modern primary voltages...APPARENTLY not. I have had this transformer for about a year ( slow project) so can't send it back
__________________
always preach the gospel-
and when necessary use words.
  Reply With Quote
Old 14th April 2008, 12:35 AM   #5
diyAudio Member
 
whitelabrat's Avatar
 
Join Date: Dec 2006
Location: Maryland
Quote:
123-124v
That's pretty high for mains. I guess the question is how to get it down then. You could adjust R34 and R35 if you're not using a choke. If you are using a choke you could implant a resistor inline to possibly lower voltage, or more dramatically, use a choke which greater resistance. It looks like you could adjust the heater voltage as well by increasing the value of R36 and R37. I'm just guessing, so you may want to confirm this.

Alternatively you could do something like what I did myself. I have a 115v mains power transformer, but my mains was at about 119 which had the voltage up a bit high. So I brought it down by dropping in a 1A isoloation transformer which when loaded caused the mains to sag down to 115V. Probably not very graceful, but it was cheap and I can pull it out of the circuit during the summer when the mains comes down to 117V.
  Reply With Quote
Old 14th April 2008, 01:26 AM   #6
diyAudio Member
 
Join Date: Jun 2005
Location: USA
Send a message via AIM to ThSpeakerDude88
our line voltage has been 121-122v for as long as I can remember, but more recently it has been hovering around 123-124v. I built a bucking reducer with taps for 110v and 117v ( cool trick with a 12.6v CT transformer, 6.3v winding acts for the 117 and full 12.6 is for 110.)

I kind of want to avoid HAVING to use such items so it would be nice if I could just get the apropriate voltage from the xfrmr. As it sits now however, I am thinking I am going to be eating a transformer and getting something more like 240-0-240 from hammond's 370 line. Their 270FX (275-0-275) gives me 405v on 120 mains, but drops to 360-380ish on 117v power. FX does not have the current capability.. I don't think...does it?)

I am seriously considering El-cheapo at this point, especially if it is sonically superior. I can get by with 10-15 UL watts easily.
__________________
always preach the gospel-
and when necessary use words.
  Reply With Quote
Old 14th April 2008, 12:28 PM   #7
Sherman is offline Sherman  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Chicago area
Quote:
Originally posted by ThSpeakerDude88
our line voltage has been 121-122v for as long as I can remember, but more recently it has been hovering around 123-124v...
I've measured my line voltage several times (dozens) over the past two years and the lowest it has ever been is 123V. I'm using a true RMS meter. The highest I've seen has been slightly over 125V and the average seems to be 124. I'm in the far west 'burbs of Chicago. Your numbers seem to match pretty well with what I've seen.
__________________
--Sherman
  Reply With Quote
Old 14th April 2008, 01:13 PM   #8
diyAudio Member
 
Join Date: Jun 2005
Location: USA
Send a message via AIM to ThSpeakerDude88
Im in indy, so its run from the ancient IPL plant. I think we really need a thread of line voltages, because these seem to be causing a lot of trouble with our vintage AND new gear since most companies seem to only want to produce transformers for 117v operation. This causes them to be noisy, run hot, and put out too much voltage for our poor amps to handle. You wouldn't think 5-8 volts would make that much of a difference but it does.

So does anyone know where I can get a NEW PA774 that really is rated for 120v operation??
__________________
always preach the gospel-
and when necessary use words.
  Reply With Quote
Old 14th April 2008, 01:47 PM   #9
w5jag is offline w5jag  United States
diyAudio Member
 
Join Date: Feb 2007
Location: Arkansas
123 ish is the typical line voltage around here.

I use a variac on some of my older ham equipment to set the correct line voltage (this is also helpful for service as you can bring devices up slowly), but, as noted above, a small bucking transformer is another easy and effective way to reduce line input voltage.

There should be lots of diagrams online as to how to wire the buck; they are pretty commonly utilized with old equipment.

Win W5JAG
  Reply With Quote
Old 14th April 2008, 02:20 PM   #10
diyAudio Member
 
whitelabrat's Avatar
 
Join Date: Dec 2006
Location: Maryland
I was planning to use an Edcor XPWR104 power transformer for my Diytube ST35. You can ask them if they have something similar with 120V primaries. They do custom work, but there may be an extra fee.

Send me an e-mail if you're interested in selling your PA774.

With regard to El-Cheapo, try holding out for Tubelab.com's latest creation. I've got a 35 6aq5's and I'm holding out to see what will happen there before I choose a circuit.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Diytube ST35 rev d whitelabrat Swap Meet 8 28th May 2010 08:36 PM
Can 6AK6's take high voltages? PRNDL Tubes / Valves 5 20th January 2009 10:06 AM
Too high transformator voltages... Skorpio Tubes / Valves 2 29th December 2008 12:21 PM
Dynaco ST35 sds2000 Tubes / Valves 31 4th January 2007 04:06 AM
Wanted: Dynaco ST35 Family Swap Meet 0 28th October 2005 04:44 AM


New To Site? Need Help?

All times are GMT. The time now is 03:13 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2