Michaelson and Austin TVA1 revB - 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 9th March 2012, 11:36 PM   #1
diyAudio Member
 
Join Date: Mar 2010
Location: MA
Default Michaelson and Austin TVA1 revB

Hi. This my first post.
I have a TVA1 that I used to run with GE 6550s with no problems. It took out a few MO KT88s until I switched to the US tube.
Anyhow, in all the photos I have ever seen, there is one small circuit board for the triodes with the octal bases visible. The amp I have has a large board that covers all tube bases. It is marked Soundlease Services Issue B. I will try post a photo. Does anyone know anything about this version? I have just bought 4 matched EH KT88s for the beast and a variac to help recharge the caps as it has been in storage for 11 years. Thanks.
Attached Images
File Type: jpg IMG-20120309-00045.jpg (531.9 KB, 283 views)

Last edited by Broncobillyo; 9th March 2012 at 11:53 PM.
  Reply With Quote
Old 9th March 2012, 11:52 PM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Welcome to the forum broncobillyo! I don't know anything about this amplifier directly, but we have plenty of UK members who can probably lend a hand.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 10th March 2012, 12:00 AM   #3
diyAudio Member
 
Join Date: Mar 2010
Location: MA
Thanks Kevin! It is a great sounding amp. I would like to rebuild it someday but the circuit has a bad rap and I wonder if it is worth the investment.
  Reply With Quote
Old 11th March 2012, 08:01 PM   #4
diyAudio Member
 
Join Date: Mar 2010
Location: MA
Default TVA1 running at half voltage

OK, so I have brought it up to half voltage - full on the variac but still config for 220V. I have yet to change the tags to 120V. I need some help with the bias. I have read that the bias resistors should be decreased in value to stop runaway with newer KT88s. Does anyone have specific info on which resistors? I assume they are on the bias board.
Thanks
  Reply With Quote
Old 28th March 2012, 03:36 PM   #5
diyAudio Member
 
Join Date: Mar 2010
Location: MA
Default Up and running

This might help someone else. The bias resistors in question are the 4 220k ones on the bias board. They are the orange ones visible in the photo. They need to be dropped to 100k to raise the -V on the grid to limit current thru the tube.
I haven't done that yet but I did replace the old black plate Brimar ECC83s and ECC81s with a new set of Sovtek 12AX7LPS (I know the drivers should be 12AT7s but I have run it before with ECC83s and it sounds leaner and more transparent in this config) and brought it up to 85V on the variac. It sounds astonishingly good.
  Reply With Quote
Old 11th February 2013, 12:27 AM   #6
diyAudio Member
 
Join Date: Jul 2009
Location: Orange Co California
Default M&A TVA-1

Hi,

Saw your questions on the TVA-1. I've got one a week ago to start up (w variac) just like yours with the big ckt board in the bottom. I haven't found much info on this one. I've seen a later version?? without the big ckt bd and a number of what apparently are copies by some Japanese Audiophiles. This apparently was a highly thought of Amp.

Wondered if you have found any more data such as cathode current, rated power out, correct ckt diag,etc. The Ckt Diagram that I've seen only generally represents this amp. Most values are different.

It has taken some time to actually get the amp running stably. At first all the outputs glowed bright red (obviously suggested a bias problem). I finally determined that the main problem was the 47uf/100v caps on the bias board. They would not reform and therefore were dragging the bias voltages down. You do not need (or want) to reduce the 220Ks. I strongly suspect you caps are bad also.

Based on the tube data, I selected 60 ma cathode current. The bias voltage needed is about -58Volts with 33ohm cathode resistors in my amp. With the caps replaced, the bias controls give a nice range and readily give the -58V. (the amp will run without the caps)

It looks like the amp may be able to handle much more cathode current.

At the 60ma, the output swings roughly 60W into 8ohms but rounded on the Positive swing.Thinking the 2 pots on the monster ckt board might adjust symmetry but they didn't do anything. Do you know how the pots are hooked into the circuit - what they are supposed to do?? It would be a major project to raise the ckt board to see how the pots are hooked in - I started but gave up!!

John
  Reply With Quote
Old 3rd March 2013, 04:54 AM   #7
diyAudio Member
 
Join Date: Mar 2010
Location: MA
John,
PM sent.
Can you post some photos?
B.
  Reply With Quote
Old 20th April 2013, 11:47 PM   #8
diyAudio Member
 
Join Date: Mar 2010
Location: MA
Default Rev B on Ebay

one for sale on Ebay, same version as mine.
This is not mine however.
Michaelson Austin TVA 1 Tube Power Amplifier Serviced Tested Works Great Clean | eBay
  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
Michaelson & Austin TVA-1 info JDeV Tubes / Valves 65 20th September 2013 02:34 AM
Revamping of a Michaelson & Austin TVA-1 gorlando Tubes / Valves 10 2nd November 2011 04:41 PM
Noisy input on Michaelson & Austin TVA-1 pix4work Tubes / Valves 4 24th September 2011 12:11 PM
Michaelson and Austin Oddysee lpd Tubes / Valves 17 10th August 2010 01:19 PM
michaelson & austin tva 10 TJ Tubes / Valves 6 24th April 2003 01:56 PM


New To Site? Need Help?

All times are GMT. The time now is 05:38 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