replace EL34 with EL37 !? - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 30th May 2012, 03:31 PM   #21
diyAudio Member
Join Date: Oct 2009
Guess he liked it.
  Reply With Quote
Old 30th May 2012, 05:40 PM   #22
rongon is offline rongon  United States
diyAudio Member
rongon's Avatar
Join Date: Jul 2009
Location: Across the river from Rip's big old tree...
Well, since you brought this thread back from the dead...

Earlier in this thread it was posited that running 6L6GC with the ST70 OPTs would result in worse performance. I was thinking that since a transformer is an impedance step-down device, what if you put your nominally 8 ohm speaker on the OPT's 4 ohm tap? That 4.3k ohm primary should now "look" like an 8.6k ohm primary, correct? I believe this halves the effective inductance of the primary, thus reducing performance at low frequencies, and reduces the output power available.

8k is mentioned as a good spot for 6L6 triode operation at lower plate voltages (say 400V plate-to-cathode). If you wanted to run 6L6 triodes into a Dyna ST70 OPT, would it be an effective strategy to connect the 8 ohm speaker to the OPT 4 ohm secondary tap?

What are the issues with this strategy?

  Reply With Quote
Old 30th May 2012, 08:34 PM   #23
diyAudio Member
Join Date: Apr 2007
Primary inductance is not affeced by the choise of secondary loading.
You will however halve the power capability of the OPT. This should not be an issue when running 6L6 in triode at 400V.

I would say go ahead.

I'm not allowed to do magic, union rules...
  Reply With Quote
Old 31st May 2012, 11:38 PM   #24
multi is offline multi  Australia
diyAudio Member
Join Date: Jan 2011
Looked up the specs for the triode connected 807 STC;{Close to 6L6 GC} at 400v Cathode bias The recommended plate load is 3000 ohms P-P. 6K p-p should work very well with 807 or 6L6GC. 807's 6L6 take a lot more drive than EL34's as triodes.
Williason used 10 K to get better Damping.
  Reply With Quote
Old 1st June 2012, 03:25 AM   #25
cerrem is offline cerrem  United States
diyAudio Member
cerrem's Avatar
Join Date: Jun 2005
Location: San Diego, CA
From all the data sheets I have seen.... The EL34 replaced the EL37 in 1954...but the EL34 was for higher voltage operation.... Looking at the plate curves and other AC they appear to be the same .....
I remember reading an article years ago from Mullard that discused this issue of the EL37 being discontinued and the EL34 replacing it for transmitter usage but with the advantage of higher voltage operation...

  Reply With Quote
Old 4th July 2012, 03:47 AM   #26
diyAudio Member
Refugee1's Avatar
Join Date: Jul 2012
Location: Worksop
Does anybody own an amplifier that was really built from new to work with the EL37?
I do and it is a bit of a pest when it comes to getting spares.
Last time i tried an EL34 it was too tall to fit my case but the sound was OK. There are a few small differences in the spec.
The older EL37s have a bigger envelope and can take a bit more before the glass melts. That is why the shape of the glass is the way it is.
If anyone wants help with guitars i would have a look at EL34s with international mains transformers for the output stages as the guys that play these instruments are more interested in the way the amplifier goes into clipping when worked hard.
Most of these guys are using EL504s with top anode caps this side of the water and also they are being manufactured again too. They sell fancy anode cap insulators for them.
Thin laminates in the output transformers is the best way to a true HI FI amplifier anyway before you choose the tubes.
  Reply With Quote
Old 24th December 2012, 01:22 PM   #27
GordonW is offline GordonW  United States
diyAudio Member
GordonW's Avatar
Join Date: Mar 2005
Location: Marietta/Moultrie GA
Originally Posted by hemgjord View Post
Primary inductance is not affeced by the choise of secondary loading.
You will however halve the power capability of the OPT. This should not be an issue when running 6L6 in triode at 400V.

I would say go ahead.

Just ran across this thread- there is one more factor, besides just the inductance, in determining performance of an output transformer, being used with impedance other than specified.

The LF cutoff of a transformer is a function of the inductance AND the output load. Just because a transformer has a certain inductance, it will NOT mean the transformer will have the same good LF performance, if the load is changed.

In fact, using a transformer, with an 8 ohm load on a 4 ohm tap, will usually degrade ultimate low-frequency performance. It will probably lose about a half-octave or so, of LF extension at full power.

OTOH- if the primary and secondary can handle the extra current- doing the opposite- running a 4 ohm speaker on an 8 ohm tap, or an 8 ohm speaker on a 16 ohm tap- can sometimes lead to an extension of the useful LF limit of the transformer, by up to a half octave.

Of course, there are other factors- including resonances, capacitance effects and such, which may mean it's not quite as simple as changing the load to half nominal value. You may run into situations, where the stability of the amp can be compromised, due to compensation networks and transformer resonant effects which may not be optimal with the new loading, without other changes in the amp as well. But, as seen by the Tronola article "Hotrodding the Eico ST70" (seen here: Hotrodding the Eico ST-70 ), it can sometimes work!

Speaker Design, Restoration and Repair- since 1985.
  Reply With Quote


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: Matched Quad E.H. EL37 Tubes Bengali Swap Meet 2 16th March 2010 10:21 PM
El34 PP Vs. El34 PSE alexmoose Tubes / Valves 47 6th September 2006 05:44 PM
Replace el34 with 6p3s ampere Tubes / Valves 1 28th March 2006 12:50 PM
EL37 ebay auction draget Swap Meet 0 9th August 2005 12:42 PM
what do I replace...? 9am53 Tubes / Valves 10 5th May 2005 02:20 AM

New To Site? Need Help?

All times are GMT. The time now is 10:25 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2