Confirmation of Primary Impedance?
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 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
 27th April 2005, 04:55 AM #1 krzanik   diyAudio Member   Join Date: Jan 2005 Location: Austin, TX Confirmation of Primary Impedance? I recently salvaged a power transformer and two single ended output transformers from an old reel to reel. I have been using guidance on the web to determine the windings ratio and subsequent primary impedance of the output transformer. I wanted to post my methodology for review and comment: -I put 125 volts (measured on the meeter) from the wall socket into the output transformer and measured 3.1 volts out. -I then divided 125 by 3.1 to determine the turns ratio and got 40:1 -I then squared the turns ratio (40 time 40) to get an impedance ratio of 1600:1 -So...if I hook this transformer up to my 8 Ohm speaker the impedance that will be reflected to the primary will be the impedance ratio (1600) times the load (8 ohms) to get a primary of 12.8 K? And if I used 4 ohm speakers the primary would be 6.4K? If someone could comment on wether I did this correctly I would be grateful. Thanks. Krzanik
 27th April 2005, 07:47 AM #2 audiousername   diyAudio Member     Join Date: Jul 2004 Location: Melbourne, Victoria Yes, your calculations appear to be correct. However, if you do them without rounding in the intermediate stages, you'll find that the primary impedance is around 13K for an 8W load (not that the difference is particularly significant). __________________ Jason
 27th April 2005, 07:47 AM #3 planet10   frugal-phile(tm) diyAudio Moderator     Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III That is correct... i'd guess EL84/6BQ5 or ECL82/6BM8 and 4 ohm speakers.... what tape deck? dave __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA
 27th April 2005, 02:44 PM #4 krzanik   diyAudio Member   Join Date: Jan 2005 Location: Austin, TX Thanks for the replies I appreciate the help. I was kind of hoping I did something wrong. Dave- you are right. the reel to reel (Ampex early 60's) was a 6BM8 with EZ81 rectifier and 12ATX driver stage. You know your tubes. I have 8Ohm speakers (fostex FE207E's) and the amp I was going to build uses 5K primary output transformers. Oh well I guess I'll have to spend some money. Any opinions on those \$16 SE output transformers (4K-10K/8watts) at Antique Electronics Supply http://www.tubesandmore.com/ ? The other choice is the \$13 5K/5watts at triode electronics http://store.yahoo.com/triodeel/tfchxfwi48oh.html . If you had your pick, which would you pick? thanks,
 27th April 2005, 05:45 PM #5 alejo   diyAudio Member   Join Date: Jun 2004 Location: bs.as. this transformers OPT is not for Hi-Fi (need 20hz-20khz). They are guitar output transformer (arround 100hz. to 15khz). Yours Fostex 207E´s is very good driver, need good Hifi OPT. See around The "UBT-2 from One Electron" in tubesandmore arround \$89.95 or HAMMOND P-T 1628SE \$97.52 if you dont take the money see general purpose Hammond P-T125SE series; not HiFi but very good irom. good build.
planet10
frugal-phile(tm)
diyAudio Moderator

Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Re: Thanks for the replies

Quote:
 Originally posted by krzanik I appreciate the help. I was kind of hoping I did something wrong. Dave- you are right. the reel to reel (Ampex early 60's) was a 6BM8 with EZ81 rectifier and 12ATX driver stage. You know your tubes. I have 8Ohm speakers (fostex FE207E's) and the amp I was going to build uses 5K primary output transformers.
Not all is lost... what amp were you going to build? The 6BM8 is limited to about 3.5W so your OPT may also be... You could build an amp with EL95s and have close to the same power & since these like really high impedance, your OPT may be fine....

BTW the 12AT7 would be the mic pre-amp tube, each 6BM8 has its own driver triode inside.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA

 28th April 2005, 07:54 AM #7 krzanik   diyAudio Member   Join Date: Jan 2005 Location: Austin, TX Not all is lost Planet 10, I was going to build the "super triode connection" 6BM8, the schematic for which can be found at the link below: http://translate.google.com/translat...lr%3D%26sa%3DG This amp caught my eye a while ago and when I came across the 6BM8's in the reel to reel I thought I'd try it. The 13K Primary output transformers I got from the reel to reel won't work with this circuit though. I looked at the EL95 and it's pretty inexpensive (cheaper than buying new output transformers) so I guess I'll start looking for schematics. 2 or 3 watts output is fine. If you have suggestions on a good circuit please let me know. Thanks.
planet10
frugal-phile(tm)
diyAudio Moderator

Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Re: Not all is lost

Quote:
 Originally posted by krzanik I was going to build the "super triode connection" 6BM8, the schematic for which can be found at the link below: http://translate.google.com/translat...lr%3D%26sa%3DG This amp caught my eye a while ago and when I came across the 6BM8's in the reel to reel I thought I'd try it. The 13K Primary output transformers I got from the reel to reel won't work with this circuit though. I looked at the EL95 and it's pretty inexpensive (cheaper than buying new output transformers) so I guess I'll start looking for schematics. 2 or 3 watts output is fine. If you have suggestions on a good circuit please let me know.
You could probably build the same circuit but with an appropriate adjectment of the cathode circuit of the pentode. Use a 12AT7 as an input tube... If you'd like to keep it to just 2 tubes use an ELL80 (likely to be not nearly as cheap).

I'm sitting on quite a few EL95s (and a few ELL80s)

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA

 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 Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post cb951303 Tubes / Valves 14 12th April 2013 05:18 AM Rob11966 Tubes / Valves 5 2nd June 2008 04:14 PM dsavitsk Tubes / Valves 16 9th February 2007 10:18 PM alexmoose Tubes / Valves 9 17th August 2006 05:34 PM

 New To Site? Need Help?

All times are GMT. The time now is 07:14 PM.