• If you have bought, sold or gained information from our Classifieds, please donate to Group DIY and give back.

    You can become a Supporting Member which comes with a decal or just click here to donate.

Transformers! transformers! Vintage transformers for tube circuits and more!

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

emrr

Well-known member
Joined
Apr 12, 2006
Messages
8,525
Location
NC, USA
up to date as of 1/2021

OK, time to let some things go so they can be put back into use.  Input, interstage, output, repeat coils, and power.  Some singles, some pairs.  In this issue:
RCA BA-3 program amp input and output transformer set
(2) RCA MI-38482 nine pin plug-in transformers (McMartin MT-4) tube inputs
Kenyon T-26 600:600
Gates console panel with 3 transformers
Presto PPP 6L6/807 tube record lathe power amp output transformer and choke
Thordarson PP 6V6 to 500 ohm output transformer pair, good for Sta-Level, etc
Tube output transformer for four 6L6
Pair of IOaudio input transformers for Pultec
RCA potted power transformers 70VCT 800mA
ADC HUM-1 video humbuckers



RCA BA-3 program amp input and UTC output transformer set
Indeed.  Both test well.  The BA-3 is a killer single ended high gain preamp with high max output level.  The UTC output is NOS, very difficult to find a high level single ended output like this with good low frequency response.  The input is in great shape. 
Input is 150/600 to grid. 
Output is for single ended 6V6 or 6L6 (RCA did both with this) to 600/150/15/7.5/5 at +30dBm with less than 1% THD 30-15K as used in a BA-3.  Lots of BA-3’s in use for vintage audio speaker listening, especially with efficient horn systems. 
$600 plus shipping/insurance on 9 lbs.
21565868612_515219e8a2_c.jpg

21577171015_d75dce7511_c.jpg



(2) RCA MI-38482 nine pin plug-in transformers
Accessory transformer for the 1970’s SA-115 transistor general use amplifier, which appears to be a rebadged McMartin unit.  A good guess would be these are rebadged McMartin MT-4’s.

https://groupdiy.com/index.php?topic=73580.msg935848;topicseen#msg935848

pins 1-3 7.5Ω DC = 125-150 pr
pins 1-4 16Ω DC - 600 pri

pins 5-6 139Ω DC = 10K bridging input

pins 8-9 91Ω DC = 10K sec
pins 2-9 349Ω DC = 60K sec

9 pin sockets frequently available NOS on ebay. 

$100 plus shipping/insurance
48948376627_9c1034c6a3_c.jpg

48948376807_306cdfb707_c.jpg


Kenyon T-26 600:600
NOS/NIB. +24db, hum bucking construction, typical multiple tap coil, see UTC A-20 impedance diagram as example.
$40 plus shipping/insurance on 2 lbs.
23474601810_24e29a38b8_z.jpg

23142118924_d0e73aed77_z.jpg

23143481483_c134bd0935_z.jpg




Gates console transformer panel
All three measure 8R : 0.7DCR roughly, would appear to be 150:speaker Z.  Possibly identical, with center piece having shielding to prevent crosstalk.  Maybe perfect for Paul’s bass trick, speaker as microphone. 
$30 plus shipping/insurance on 3 lbs.
16266225548_1e0977859c_c.jpg

16452178541_67af6e5e00_c.jpg



Presto tube record lathe power amp output transformer and choke
From a model 88-A power amp, using (4) 6L6/807 type power tubes.  Has plate cap attachment for use with 807 tubes, can be removed for standard wiring to 6L6’s.  Also the transformers on the later 92-A/B models, which spec within 1dB 20-17K. output impedances of 500/250/15/6 ohms at 50W output.  Choke is 10H.  The last picture shows how it was used on the 92-A amp, with plate cap attachment.
http://www.hifido.co.jp/KW/G0105/E/0-50/C05-23362-51346-00/
http://www.steveespinola.com/lathetrolls/resources/Presto_92A_Manual_Schematic_gif.pdf
$200 plus shipping/insurance on some lbs; heavy.
15833866673_d5519f4ede_c.jpg

15833864933_f439f373c1_c.jpg

15833863473_e4cbf60794_c.jpg

16487748196_8cbda85cf1_c.jpg



(2) Thordarson PP 6V6 to 500 ohm output transformers
Great for Stalevel and other tube limiters or compressors.  T-17S11.  One is on a sub-panel which has a rotary switch to choose output impedances from 500/25016/8/4.  Rated 15W, primary 8K. 
$150 plus shipping/insurance on 7 lbs.
16486025462_44a3e41b73_c.jpg

16461004276_b78360c3f7_c.jpg

16299565030_155c544165_c.jpg



Tube output transformer for four 6L6
Apparently from a Baldwin organ with several references suggesting 40W power, tests fine for DCR, leads in good condition.  Nice hefty chunk of iron for a power amp build.  Part #512-14633D.  Organs have to pass some low lows, so inductance should be better than average. 
$40 plus shipping/insurance on 5 lbs
16454557165_f902258dcb_c.jpg

16452806571_16837accf6_c.jpg



Pair of IOaudio input transformers for Pultec
As provided with his MEQ500 mid range Pultec project back in 2008 or so.  They didn’t work for me as I was trying to use them with true 600 ohm source impedances, and they are somewhat rolled off on the bottom in that case.  Feed them with a 50 ohm source such as many converters provide today, and they are full range on the bottom, with IOaudio measuring a -3dB point of 14Hz in that case. 
$20 plus shipping/insurance on 1 lb.
5433355497_eeac6b29a8_z.jpg



RCA potted power transformers 70VCT 800mA
Multiple pieces of very nice potted/shielded power transformers for SS projects.  Two are US voltage only, seven more that cover international voltage ranges. 
$25/ea plus shipping/insurance on 5 lbs.
16299292148_03a99d6de4_z.jpg

16485253371_c1ff96345c_z.jpg



ADC HUM-1 video humbuckers
Off the audio path, into video.  I have a number of these to sell.  New in original shipping boxes.  BNC connectors.  Pass audio too, an interesting euphonic sound, probably from the low 75Ω loading. 

Here's a typical ad for one at $160: 
http://www.markertek.com/product/hum-1/adc-by-te-connectivity-hum-1-humbucking-coil

$30 + shipping and insurance.  Slightly under 4 lbs / 1.8 kg shipping weight per piece.

4126928866_e5eaf343b0_o.jpg




---------recently sold-----------

UTC A-20
has some paint pulled off from tape, has connection labels added on side, with an original A-20 box.  Tests fine.
$50 plus shipping/insurance
48948181256_fa0fc5fea4_c.jpg


RCA OP-6 tube mic preamp input transformer pair
RCA OP-6 input transformer pair in good shape, ready to go into your two channel tube mic preamp build.  Typical American impedance ratios of 30/250Ω to single tube grid use, center tap also available on the primary.  Great classic sound.  Tested for both resistance and inductance. 
$295 plus shipping/insurance on 2 lbs. 
39455063941_387a73cdb0_z.jpg


39455061981_4920024326_z.jpg


39455064841_3918fa0be3_z.jpg



 
emrr said:
OK, time to let some things go so they can be put back into use.  Input, interstage, output, and repeat coils.  Some singles, some pairs. 

UTC HA-108 600:600 transformer A-20 upgrade
Repeat coil like A-20 and LS-30, early shiny black type with rectangular terminal layout.
$70 plus shipping on 2lb. 
I'll take the HA-108, so long as the shipping isn't high.  Please PM me with payment instructions at your convenience.  Location; Phoenix, AZ. 85032.
Thanks!
 
Aaargh, I give up! The OP6 inputs look perfect, time to finish that stereo RCA-style preamp. Still have them? Shipping to Sweden. :)

Best
/Dave
 
Received the A20s today. Excellent packing and excellent condition transformers. Thanks Doug! After reading a few 100 of your posts on various message boards, its nice to put some moolah in your pocket!  ;D
 
Back
Top