Problem with my ST70 build - 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 12th April 2008, 10:52 PM   #1
JayH3 is offline JayH3  United States
diyAudio Member
 
Join Date: Mar 2008
Default Problem with my ST70 build

I just finished my ST70 build and powed it up. I dont blow any fuses and the tubes glow with none of them being dimmer or brighter than the others.

The problem is that I have no output.

I am checking over everything again but was wondering if anyone had any suggestions on where to pay special attention.

Im also a little confused on how the 500k pots should be set because the diytube.com instructions make no mention of them.
  Reply With Quote
Old 12th April 2008, 11:15 PM   #2
JayH3 is offline JayH3  United States
diyAudio Member
 
Join Date: Mar 2008
I thought that I possibly had the bias pot wires switched around so I swapped them.

Now when I hook up my meter to bias I hear static out of the speakers.

I also have a faint hum now from the speakers, so I think I am on the right track. The problem must be in the input section. I will be looking for a problem there, still open to suggestions, though.
  Reply With Quote
Old 12th April 2008, 11:57 PM   #3
diyAudio Member
 
Ty_Bower's Avatar
 
Join Date: Mar 2007
Location: Newark, DE
You'll need to check the voltages against the chart in the manual. Post your results here, and maybe someone can spot the problem. Be sure to make a post on the diytube.com forum as well.

A hi-res photo of the board and wiring wouldn't hurt, either.

In a perfect world, the 500k pots on the driver board should be set exactly in the middle. They balance the bias voltage to each side of the push/pull pair of output tubes. If the tubes are well matched, the pot should end up pretty close to centered.

I think the pot is a ten-turn job. Trying to center it by counting turns would be tricky. You could probably meter it out (with the power off) and check to see if each side is roughly 250k.
  Reply With Quote
Old 13th April 2008, 03:55 AM   #4
JayH3 is offline JayH3  United States
diyAudio Member
 
Join Date: Mar 2008
I think the battery may be going in my meter. Its acting kinda strange.

But, the highest voltage I read on the whole amp was 30VDC, even on the power supply board.

I think the project has to go on hold for a little while - one of the bias pot pins broke off.
  Reply With Quote
Old 13th April 2008, 11:58 AM   #5
diyAudio Member
 
Join Date: Nov 2002
Pictures would help.

Also, what driver board did you use? Is this a rebuild of a stock Dynaco or is it an aftermarket kit?
  Reply With Quote
Old 13th April 2008, 01:57 PM   #6
JayH3 is offline JayH3  United States
diyAudio Member
 
Join Date: Mar 2008
Quote:
Originally posted by burnedfingers
Pictures would help.

Also, what driver board did you use? Is this a rebuild of a stock Dynaco or is it an aftermarket kit?

Its all aftermarket. For the power supply section I bought triodeel.coms board. For the driver board I built the diytube.com board using point to point wiring.

As for a picture...Ill admit, I got too small of an enclosure so even the most knowledgable expert would have trouble looking at a picure of this nest of wires. Im proud to say even working in such small spaces and using a large soldering gun I did not burn any wires insulation.
  Reply With Quote
Old 13th April 2008, 07:40 PM   #7
JayH3 is offline JayH3  United States
diyAudio Member
 
Join Date: Mar 2008
I just replaced the bias pots and got a new battery for my meter.

I took some measurements and I cant get any bias voltage and all of the pins with high dc voltage is up over 500VDC.

On the el34's I am supposed to get -35V on two spots. I get it on one but not the other. (actually, the voltage chart says pins 5 and 6 but 6 is not used so I am probably ok here.)

On the power supply board the 300 and 350VDC lugs are reading over 500VDC.

Any ideas? Thanks for any input.
  Reply With Quote
Old 13th April 2008, 10:53 PM   #8
diyAudio Member
 
Join Date: Nov 2002
Borrow a digital camera and post some pictures. It would be a lot easier to figure out the wiring problems.
  Reply With Quote
Old 13th April 2008, 11:13 PM   #9
diyAudio Member
 
Join Date: Nov 2002
Is this the power supply board?
Attached Images
File Type: jpg p4130030.jpg (59.9 KB, 203 views)
  Reply With Quote
Old 13th April 2008, 11:17 PM   #10
JayH3 is offline JayH3  United States
diyAudio Member
 
Join Date: Mar 2008
Quote:
Originally posted by burnedfingers
Is this the power supply board?

Yes, thats the one I am using.

This is the drive board section. http://www.diytube.com/st70/diytube_st70_B.pdf

One of my probes for my meter broke so another setback. Ill have to wait until I can grab my other one from work tommorrow to take more measurements.
  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
DIY Dynaco ST70 wingking3000 Tubes / Valves 2 25th July 2008 10:20 PM
Need help with my ST70 JayH3 Tubes / Valves 7 23rd May 2008 12:56 AM
Power Amp Build from Eico ST70 - Negative Feedback Question Vespasian Tubes / Valves 15 5th February 2007 05:40 AM
Help on deciding what to build - problem room. Emprov Multi-Way 2 25th August 2005 04:50 PM
Dynaco ST70 cwteoh Tubes / Valves 14 27th May 2004 06:07 AM


New To Site? Need Help?

All times are GMT. The time now is 11:00 PM.


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