Frequency response of my Darling

sweet & juicy SE amp for 1626 Darlings and the 6L6 family

Frequency response of my Darling

Postby MKJ » Wed Aug 01, 2012 5:17 am

Hallo,

here's the FR curve for my Darling (12SL7/1626). I use vintage Telefunken output transformers (12k-5R), which are reasonably priced and easily available in Germany. That doesn't look bad all. I had expected a worse FR on the low end:

Image

30 to 20.000 Hz (-3dB) is quite ok for me. And this is my Darling tube amp with an external PSU.

Image

Mike
MKJ
 
Posts: 20
Joined: Thu Jul 12, 2012 6:19 am

Postby Shannon Parks » Wed Aug 01, 2012 6:00 am

Thanks for the frequency sweeps, Mike. Here's my earlier Darling sweeps for comparison (several posts down):
http://www.diytube.com/phpBB2/viewtopic.php?t=4970

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Postby MKJ » Wed Aug 01, 2012 6:21 am

Shannon, thanks for the link. Very nice FRs! Congratulations! I'm pretty sure that the output transformer is the weakest part in my Darling. Unfortunately, I don't know a supplier for budget iron (in Germany). New transformers are 50-70 USD each. What equipment do you use for your frequency sweeps? It's obviously not a soundcard. Do you use a PC for recording the results?

Mike
MKJ
 
Posts: 20
Joined: Thu Jul 12, 2012 6:19 am

Postby Shannon Parks » Wed Aug 01, 2012 6:43 am

No prob. I use a Boonton 1120 Audio Analyzer with software I wrote in vb.net for plots to MS Excel. Similar devices are the Boonton 1121, the HP 8903A and the HP 8903B. Pete Millett uses the 8903B.

If you had plenty of gain, you could always add some global feedback, though you would have to mod the V1 biasing to be like the ULtras. Stability is not an issue with these two stage amps, so you can add as much or as little feedback without worrying about the stability. Your damping would go up, too.

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Postby MKJ » Wed Aug 01, 2012 7:01 am

separks wrote:I use a Boonton 1120 Audio Analyzer with software I wrote in vb.net for plots to MS Excel.

Fantastic setup. I envy you! Thanks for the information.
Mike
MKJ
 
Posts: 20
Joined: Thu Jul 12, 2012 6:19 am

Postby EWBrown » Wed Aug 01, 2012 8:11 am

Those vintage Telefunken OPTs are pretty good, I've used them in 12B4A and 6S4A SET designs. If you really like to have a high effective (reflected) primary impedance, use these with 8 ohm speakers [:)

I have been getting mine from the e-place, "tested tubes" in Germany

/ed B
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Postby MKJ » Wed Aug 01, 2012 8:37 am

I agree with you, and I like the Telefunken stuff (I was born in Hannover, where the Telefunken head office was.) Problem is, that the quality is not consistent. I've found differences of up to 3dB below 100 Hz between vintage OTs. The air gap of SE OTs might be a problem. Some days ago I tried Saba OTs. On paper they are perfect with a 7k primary impedance. In reality they weren't:

Image

Don't know what's wrong here (yellow curve = Saba OT). 8 ohms speakers are not really an option for me. I love my Saba Greencones that are a good match for the low power Darling (104 dB efficiency!). The Sabas are 4-5 ohms drivers.
Interestingly, I didn't like the excellent Philips 9710 driver in combination with the Darling. Probably, the 9710 needs more power than the Darling can provide.
MKJ
 
Posts: 20
Joined: Thu Jul 12, 2012 6:19 am

Postby MKJ » Sun Aug 05, 2012 9:08 am

Shannon,

which Edcor OT do you use? Is it the XSE or the GXSE series?

Mike
MKJ
 
Posts: 20
Joined: Thu Jul 12, 2012 6:19 am

Postby Shannon Parks » Sun Aug 05, 2012 10:23 am

MKJ wrote:Shannon,

which Edcor OT do you use? Is it the XSE or the GXSE series?

Mike


I use the GXSE15 series. They have the most inductance. I think you can search the forums for some inductance tests that Ed Brown did.

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Postby MKJ » Sun Aug 05, 2012 11:22 am

Shannon,

thanks for the information. The GXSE series would have been my choice. Too bad that shipping is so expensive. The Edcor OTs seem to be very good products.

Mike
MKJ
 
Posts: 20
Joined: Thu Jul 12, 2012 6:19 am

Postby MKJ » Mon Aug 06, 2012 2:10 pm

EWBrown wrote:Those vintage Telefunken OPTs are pretty good, I've used them in 12B4A and 6S4A SET designs.

They are, indeed. But you have to be careful. Today, I've received two Telefunken SE OTs (7k-4R). FR was just awful:

Image

It's a nuisance that german sellers always say "tested" and "fully working". No, they don't test at all! They grab an old tube radio and switch it on. "We hear anything? OK, it's working! Let`s get everything out of it and sell it on Ebay!"
Even the "tested tubes" seller claims that he measured 4R and 12K resistances using his multimeter. That's simply impossible with DC measurements. I bought from him recently and will post the results. So, be careful and be lucky that you can buy from Edcor.
MKJ
 
Posts: 20
Joined: Thu Jul 12, 2012 6:19 am


Return to clementine

Who is online

Users browsing this forum: No registered users and 21 guests