EICO HF-30 - Schematic - 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 10th October 2010, 07:32 PM   #1
bigger is offline bigger  Canada
diyAudio Member
 
Join Date: Sep 2010
Default EICO HF-30 - Schematic

I am in the process of collecting parts to clone a pair of HF-30's. I have been able to find some schematics, but they are conflicting.

The schematic that I have from Eico shows the driver tubes as 6AV6 and 6C4, but the schematic I have from Photofact shows a single driver tube using the 7247.

I assume that during productioin of this amplifier, Eico switched to the 7247, which I am told was design manufactured for them.

What I would like to know, has anyone compared the 2 versions of this amplifier?

Any advise or opinions are welcomed!

Big
  Reply With Quote
Old 10th October 2010, 10:44 PM   #2
pchw is offline pchw  United States
diyAudio Member
 
Join Date: Apr 2006
Location: Fremont, California
The 7247 is essentially the other 2 tubes in one bottle. Pretty much the same circuit from the component properties perspective.
__________________
- Fred -
  Reply With Quote
Old 10th October 2010, 11:45 PM   #3
TheGimp is offline TheGimp  United States
diyAudio Member
 
TheGimp's Avatar
 
Join Date: Aug 2009
Location: Johnson City, TN
Check out the Eico group on Yahoo. Lots of knowledge there.
  Reply With Quote
Old 11th October 2010, 01:19 AM   #4
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I owned a pair of the HF-30 using the 6AV6/6C4 driver, and a more mediocre sounding 6BQ5 amplifier design I have not heard.. (In fairness the transformers were not that great, but the overall design is one big, cheap compromise IMNSHO..) if you are going to all the trouble of building an amplifier like this I would choose something else as the basis for the design.. I've no objection to PPP at all, just this particular design.

Perhaps Eli or SY can steer you in the direction of a design worthy of your construction effort, or they may disagree totally with my opinion.

The old Acrosound 2020 design might be worth considering if you are up for a real challenge. IMHO this is the best sounding 6BQ5 I have heard, but it might be tricky to get working at all as a PPP amp, and the compensation may be problematic as well..
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 11th October 2010, 02:00 AM   #5
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Quote:
Originally Posted by kevinkr View Post

they may disagree totally with my opinion.
Nope, I wouldn't. Eli has published an excellent design that will fit in there. So have I. And, sous entendu, the Bevois Valley design by Morgan Jones would be a top candidate for a rebuild.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 11th October 2010, 02:15 AM   #6
bigger is offline bigger  Canada
diyAudio Member
 
Join Date: Sep 2010
Thanks for the input. BTW I don't believe the 7247 is the 6AV6 and 6C4 in 1 tube, I believe it's 1/2 a 12AX7 and 1/2 a 12AU7.

I am looking to use some very nice 4K3 outputs (big massive iron - rated at 50W - I have 3 pairs), I don't want to use EL34's so I thought PPP EL84's would be nice (I also have a large stock of EL84's)

Where would I find the designs by SY or ELI?

Thanks

Big
  Reply With Quote
Old 11th October 2010, 03:00 AM   #7
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
Thanks for the input. BTW I don't believe the 7247 is the 6AV6 and 6C4 in 1 tube, I believe it's 1/2 a 12AX7 and 1/2 a 12AU7.
Your belief is incorrect. The 7247/12DW7 is an asymmetrical twin triode, where 1 section is like the triodes found in the 12AX7 and the 2nd triode is like those found in the 12AU7. The 6AV6 is triode/dual diode. The triode in the 6AV6 is like the triodes in a 12AX7. The triode in a 6C4 is like the triodes in a 12AU7.

Quote:
I am looking to use some very nice 4K3 outputs (big massive iron - rated at 50W - I have 3 pairs), I don't want to use EL34's so I thought PPP EL84's would be nice (I also have a large stock of EL84's)
PPP EL84s will work with your "iron". You will need to use "fixed" bias and an individual trim pot. for each EL84.

SY's design is named "Red Light District". Search the archives for details. FWIW, my design is named "El Cheapo". I've uploaded the schematic for your consideration.

If follow the "El Cheapo" model, buffer the LTP with DC coupled ZVN0545A source followers. "Fixed" bias has a lower grid to ground resistance limit than cathode bias does. You will not get the gain you need, without help from FETs.
Attached Images
File Type: gif ElCheapo-23jun06-map.gif (36.3 KB, 123 views)
__________________
Eli D.
  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
Eico HF-86 service_guy Tubes / Valves 1 21st February 2010 11:11 PM
Eico HF-32 crick Parts 3 25th June 2007 02:18 AM
Eico hf-30 reworking fortytwo Tubes / Valves 5 4th March 2006 01:51 AM
Any comments on Eico HF-14 and HF-85 percy Tubes / Valves 5 13th January 2005 01:11 AM


New To Site? Need Help?

All times are GMT. The time now is 05:11 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