Quad query - 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 6th December 2012, 04:51 PM   #1
diyAudio Member
 
Join Date: Jun 2004
Location: Sussex, England
Default Quad query

Flat earthers look away now! I've rebuilt my prevoiusly working Quad 11 power amps- rewire, new sockets 60uf smoothing before and after choke, GZ34 rectifier. All works well except I'm having to use an auto transformer to keep the operating voltages as specified (340v o/p stage, 330v input/driver, 6.3v heater).
When I use the 240v/com transformer taps as normal for uk supply and run from 240v mains, the TH rises to about 380v and heater 6.6v and the KT66s start to suffer! Does the combination of GZ34+extra reservoir capacity compared with the original GZ32 16+16uf account for this? The only fly in the ointment is the ac heater voltage is higher too. Any ideas?

Cheers

Matt
  Reply With Quote
Old 6th December 2012, 05:13 PM   #2
diyAudio Member
 
indianajo's Avatar
 
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
Wall voltages are higher than they used to be. Since the higher voltage cuts transmission losses, they are not going down either, unless your building goes on local wind power inverters or natural gas fuel cell supplied electricity.
If your voltages are over the tube datasheet maximums, the 1950's technology to reduce B+ or A (heater) voltage was 1 watt or 1/2 watt carbon comp resistors. I tend to buy metal film resistors as the premium product these days (vishay or multicomp) but you have to buy the 2 to 3 watt variety to get length long enough to sustain tube voltages over time dust & moisture. Wirewound 3 watt resistors are also long enough. If you don't have a can cap to mount them on, turret board from guitar amp builder supplies is probably the best you can get in europe. I can get solder type terminals strips copies of cinch jones designs from electronicsurplus.com in NY or triodeelectronics.com in IL, but the shipping and customs to Europe would be excessive. I haven't seen these in europe. If you have to drill holes in the metal for a mount screw, magnetize the drill bit and use a magnet near the hole to pick up the metal trash. If you have a steel chassis. Otherwise, clean, clean, clean.
If you don't want to vent the heat, a 240-220 VAC single phase transformer is in order. Or maybe cheaper, a different power transformer designed for modern power.
If your plate voltage are within limits but the plate dissipation wattages are too high, you can turn down the idle current from stock to get the wattages under control. Red plates is good for nasty sounding guitar amps, but not for hifidelity.
__________________
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

Last edited by indianajo; 6th December 2012 at 05:33 PM.
  Reply With Quote
Old 6th December 2012, 06:14 PM   #3
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
The GZ34 may drop a bit less voltage. The extra reservoir capacitance will boost voltage a bit too.

In (EU legal) theory the UK mains should edge down to 230V. In (real life engineering) practice it is more likely to edge upwards for the reasons given by indianajo.

Heaters being 5% high and HT being 10% high suggests both effects are in play.
  Reply With Quote
Old 6th December 2012, 10:30 PM   #4
diyAudio Member
 
Join Date: Jun 2004
Location: Sussex, England
Thanks for the replies. DF96- I'm feeding the quad with 240v from a variac into the 240v taps on the mains transformer, so it should out put the correct voltage on the secondary. That's why I'm confused.
indianajo- thanks I think reducing the quiescent current is a good idea. I'm just confused as to why the amp seemed top work reliably before I reworked it.

Cheers

Matt
  Reply With Quote
Old 7th December 2012, 09:50 AM   #5
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
I'm just confused as to why the amp seemed top work reliably before I reworked it.
I wish I had a fiver for everytime I heard someone say that! (or its equivalent for software development)
  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
RARE QUAD ESL57 ORIGINAL QUAD UK TREBLE PANELS - PAIR lampes Swap Meet 3 6th December 2012 09:02 PM
FS:NOS 1954 Philips EL34 metal base quad 4 100% emission very rare quad EL34. ivershing Swap Meet 0 17th August 2012 02:07 PM
Quad II/ Quad 22 parts/ parts units WANTED hatrack71 Swap Meet 0 3rd March 2011 01:05 PM
WTB: Any Quad II or Quad 22 units- working or not or parts for them hatrack71 Swap Meet 3 29th August 2010 02:46 PM
FS: Ei/Yugo KT90 quad, 6H30, svet KT88 quad - melbourne avian Swap Meet 9 15th April 2010 06:46 PM


New To Site? Need Help?

All times are GMT. The time now is 08:42 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