What can I build with this iron? - 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 22nd March 2005, 12:00 AM   #1
diyAudio Member
 
leadbelly's Avatar
 
Join Date: Dec 2002
Location: Calgary, Alberta
Default What can I build with this iron?

I bought an old Knight KN-720 amp as a donor to build a new amp from. The amp is a PP 6V6GT design. The picture shows the transformers, basically it is a 620VCT power tranny and two output trannies with 190 ohms between taps.

I am looking for some recommendations/links/schematics for an amp I can build using this iron. No need to reuse any of the original tubes, not even the rectifier. I am not picky about power required as I will build efficient speakers. I am not resistant to silicon and would likely put an SS regulator in no matter what the original design called for. Not afraid of a complex design, as a matter of fact I would probably prefer it. Does not even have to be an integrated amp, I can drive it with this preamp:

http://www.diyaudio.com/forums/showt...590#post601590

So as you can see, I am wide open to suggestions. I am more looking for a "this amp is a killer" recommendation than "this amp is a good starter" advice. I just don't know enough about tubes & transformers to know what I can build with those output trannies!
Attached Images
File Type: jpg knight iron.jpg (23.3 KB, 473 views)
__________________
Aerodynamics are for people who can't build engines. Enzo Ferrari
  Reply With Quote
Old 22nd March 2005, 12:27 AM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Just guessing here- this is probably a 8K plate-plate opt (you should verify this!). Besides 6V6, it should work very nicely with 6BQ5/EL84. And there's a TON of designs out there with that tube; I'm building one myself at the moment. Figure a solid 10-12 watts in pentode or UL mode. If you want something a bit more challenging, a pair of 6BL7/6BX7 should give you 10 watts of pure triode.

The Bevois Valley amp in Morgan Jones's "Valve Amplifiers" is a nice, simple, classic design, and has the benefit of a full engineering analysis in the accompanying text.

edit: I see that this tranny doesn't have UL taps, so you'll need to decide between pentode and triode.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 22nd March 2005, 12:40 AM   #3
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
LB,

Those O/P trafos were used with 6V6s and there is no reason to change. However, you could use EL84s.

Surf on over to Audio Asylum (www.audioasylum.com). Search the Tube DIY Forum archives for posts by "Poindexter". Poinz has an elegant triode wired PP 6V6 circuit that's exactly what you need.

On the PSU front, the higher voltage SS rectification yields would give you the headroom you need for regulation. Even though they are costly, use 1200 PIV Silicon Carbide (SiC) Schottky diodes, as they are DEAD QUIET.
__________________
Eli D.
  Reply With Quote
Old 22nd March 2005, 12:21 PM   #4
diyAudio Member
 
Join Date: Sep 2003
Location: London
I have a Leak Stereo 20 with an 8K OPT, and by far the best sound I've had from this is using two pairs of 6S4A triodes in push-pull. These are very cheap and plentiful in NOS, and genuine triodes, not triode strapped pentodes, and they're also easy to drive because their amplification factor is around 16 and they're good for 8.5w dissipation. Also the heater requirement is modest - .6amp, and since they run at 20mA in existing EL84 designs, two of them neatly slot in for single EL84s or 6V6s. Plus you get about double the output of a single EL84 in triode. I run them in fixed bias and drive them from a diff pair of 6BK7 (a ECC88 type) with one of Morgan Jones constant current sinks underneath. If you listen to classical music or jazz, the grand piano sound is particularly good and realistic, which is a joy to me since I listen a lot to that. I have a circuit I can email. Andy
  Reply With Quote
Old 22nd March 2005, 03:21 PM   #5
diyAudio Member
 
leadbelly's Avatar
 
Join Date: Dec 2002
Location: Calgary, Alberta
Thanks for all your leads.

In reviewing the amps you guys referred to, I noticed that my OPT's are noticeably smaller than those used in the amps you mentioned. Does that impact best tube choice in some way? What I mean is would that steer me towards the EL34 which some say has better bass, in order to offset what is likely weak bass from my OPT's? Or just the opposite: give up on making a fullrange amp and use the 6V6 to make a smoother midrange + tweeter amp?
__________________
Aerodynamics are for people who can't build engines. Enzo Ferrari
  Reply With Quote
Old 22nd March 2005, 06:21 PM   #6
danhei is offline danhei  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Denver, CO
Andy,
I would be interested in seeing that schematic if you get a chance. My email is dan636@yahoo.com

I've built guitar amps but want to build a good stereo amp soon.

Thanks, Dan
  Reply With Quote
Old 23rd March 2005, 12:20 AM   #7
diyAudio Member
 
Tom Bavis's Avatar
 
Join Date: Jun 2002
Location: Macedon NY
According to the Sams parts list, the output transformers are 8400 Ohms to 4 and 8 Ohms. They are rather small, so that will limit the bass. Triodes will give a little more low end, but transformer saturation will be the real limit.

Build it! But leave room for better transformers if you decide to upgrade later.
  Reply With Quote
Old 30th March 2005, 05:01 PM   #8
diyAudio Member
 
leadbelly's Avatar
 
Join Date: Dec 2002
Location: Calgary, Alberta
OK, after mulling it over I think I would like to use triode strapped SV83's. I think I will only build the output stage and use my already completed 6922 preamp to drive it. This will leave me a lot of flexibility to try different front ends in the future.

With the huge number of EL34 schematics out there, I thought I would have an easy time finding exactly what I wanted, PP triode strapped, CCS bias. I have not found one like this so far. What's up with that? Is CCS bad for the EL34?

Another question is that I have been told to strap the screen grid to the plate with a resistor. Is the screen grid G2 or G3? Here's the pinout:
Attached Images
File Type: jpg sv83 pinout.jpg (9.9 KB, 172 views)
__________________
Aerodynamics are for people who can't build engines. Enzo Ferrari
  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
FS: Tubes and Iron N1ESE Swap Meet 5 29th November 2008 01:30 AM
Gun or Iron? mashaffer Tubes / Valves 13 29th December 2007 01:22 PM
HOT Iron ? Vespasian Tubes / Valves 23 2nd November 2006 12:36 AM
build my first full ranger,let's build another one:a small fullrange high end pc-spea then_dude Full Range 2 30th November 2005 07:54 AM
Do i need to build main supply (240v) filter?Or build power distribution? thomgun_lc Chip Amps 9 16th September 2005 09:52 AM


New To Site? Need Help?

All times are GMT. The time now is 05:27 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