Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki 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

Need RIAA phono preamp based on octal or ST
Need RIAA phono preamp based on octal or ST
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 1st February 2019, 04:29 PM   #11
leadfinger is offline leadfinger  United States
diyAudio Member
 
Join Date: May 2007
Location: Northeast Ohio
You might check out the cornet Octal...

http://www.hagtech.com/pdf/cornetoctal.pdf
  Reply With Quote
Old 2nd February 2019, 01:32 AM   #12
Mr_Zenith is offline Mr_Zenith  United States
diyAudio Member
 
Mr_Zenith's Avatar
 
Join Date: Aug 2009
Location: KC Metro
Need RIAA phono preamp based on octal or ST
It's interesting this thread should come up, as I've been considering a scratch-built RIAA stage build over the past week. The three I'm considering:

I've already gathered the parts for Eli's stage, which I like for its novel approach, but I was wondering about the pros and cons of the other two. The JE Labs is attractive because I have boatloads of NOS Loktals, but Vinylsavor's looks to be simpler.

Just want to see what others think here...
  Reply With Quote
Old 2nd February 2019, 01:57 AM   #13
craigtone is offline craigtone  United States
diyAudio Member
 
craigtone's Avatar
 
Join Date: Apr 2006
Location: Holland, MI
Here is another option:

Tavish 6SL7 Phono build
__________________
Craigtone Audio
Soundsmith Boheme, WT Classic, Pearl 2, Apollo-R, D100 Mk2, Hafler 915, TSE 45, ALK Klipschorns
  Reply With Quote
Old 2nd February 2019, 02:31 AM   #14
Eli Duttman is offline Eli Duttman  United States
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
I have boatloads of NOS Loktals
Got 7F7s or 14N7s? Very little in the way of changes would be needed to use those Loctals in the tweaked RCA setup.

Another "frisky" parts from the "pile" tube complement would be a Russian 6H2Π (6n2p) for the 1st gain blocks and a 6SC7 for the 2nd gain blocks.
__________________
Eli D.
  Reply With Quote
Old 2nd February 2019, 08:29 AM   #15
Mr_Zenith is offline Mr_Zenith  United States
diyAudio Member
 
Mr_Zenith's Avatar
 
Join Date: Aug 2009
Location: KC Metro
Need RIAA phono preamp based on octal or ST
That was going to be my next question (you read my mind). And since the 7F7 is basically a Loktal 6SL7, this might further expand the options for the OP. I've considered the 7F7/6SL7 as a substitute, but was concerned with the different interelectrode capacitance and Mu (the 7F7's 70 vs. 100 for the 12AX7).

I'm fairly handy with flush cutters and a soldering iron, but like the OP my eyesight ain't what it used to be.
  Reply With Quote
Old 2nd February 2019, 10:08 AM   #16
Eli Duttman is offline Eli Duttman  United States
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
I've considered the 7F7/6SL7 as a substitute, but was concerned with the different interelectrode capacitance and Mu (the 7F7's 70 vs. 100 for the 12AX7).
Remember, net gain is controlled by both μ and RP. There's not much difference between the 'X7 and the 'SL7, when you crunch the numbers.
__________________
Eli D.
  Reply With Quote
Old 2nd February 2019, 10:29 AM   #17
Greg Hyatt is offline Greg Hyatt  United States
diyAudio Member
 
Join Date: Jul 2017
JE rejected the 7B4 because it is a single triode and did not fit his chassis, but it seems to be a direct replacement for the 12AX7 in ratings. Even the capacitances are similar when you recognize that the 7B4 seems to always be measured with a shield, and the 12AX7 without. I don't mind having a forest of tubes, it was -22 F here in northern IL yesterday and my furnace could use the help! So unless someone points out a problem I have missed I will build one of the 12AX7 circuits with the 7B4. The question is which one...
  Reply With Quote
Old 2nd February 2019, 10:52 AM   #18
Eli Duttman is offline Eli Duttman  United States
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
So unless someone points out a problem I have missed I will build one of the 12AX7 circuits with the 7B4.
I would not regard 4 bottles as a "forest". What you have to watch out for in passive EQ setups is matching. Well matched triodes are needed in the channel to channel corresponding positions. Matching of the triodes in a channel is not necessary.
__________________
Eli D.
  Reply With Quote
Old 2nd February 2019, 05:48 PM   #19
Greg Hyatt is offline Greg Hyatt  United States
diyAudio Member
 
Join Date: Jul 2017
My listing room is not balanced so I guess the tone-stack could take care of miss-matched triodes at the same time?
I have been looking for an excuse to use glow-discharge tubes for the first time, so how about the following for the power supply?

Sticking with the Loktal the 7Z4 makes an inexpensive voltage multiplier. The caps should give me about 300v to fire the regulators (with the 1meg shunt to help).
The 68k resistor is just to drain the caps when powered off for safety.
The 22k resistor limits current through the glow-tubes
x notes the path to remove voltage from the circuit with removal of a regulator.
.1uf should be small enough to prevent oscillation while providing some filtering.

Suggestions?
Attached Images
File Type: png Picture1.png (36.3 KB, 318 views)
  Reply With Quote
Old 3rd February 2019, 06:16 AM   #20
Eli Duttman is offline Eli Duttman  United States
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
I say, did somebody mention voltage doubler? The attached "hen scratch" schematic is inexpensive to execute and would work well with gas discharge regulation.

BTW, the 0.1 μF. noise suppression part is (IMO) pressing your luck, with regards to observing unwanted relaxation oscillator behavior. I think 0.068 μF. is a better choice.
Attached Images
File Type: jpg 117Z6 PSU.jpg (334.2 KB, 263 views)
__________________
Eli D.
  Reply With Quote

Reply


Need RIAA phono preamp based on octal or STHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Little-Bear Tube Phono RIAA Preamp john65b Swap Meet 5 Yesterday 08:14 PM
Need good EF86 based RIAA preamp. Black Jack Tubes / Valves 61 10th February 2015 09:54 AM
Groovewatt-Valve RIAA Phono Preamp? livingdeliberately Tubes / Valves 9 24th April 2014 02:16 AM
Hi-Fi RIAA Phono Preamp zoltan777 Solid State 6 4th November 2013 05:21 PM
Noise on the RIAA phono preAmp diarav Chip Amps 3 23rd March 2007 05:27 AM


New To Site? Need Help?

All times are GMT. The time now is 09:01 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki