letterbeacon

Re: rainton's True To The Original PULTEC EQP1-A chassis kit discussion thread
« Reply #120 on: December 21, 2017, 10:41:54 AM »
This is a basic question, but how do you mount the can capacitors to the back panel? In the past I've used clamps, but it seems people are using sockets which look much cleaner. Can anyone link me to the sockets that people are using?


hugo

Re: rainton's True To The Original PULTEC EQP1-A chassis kit discussion thread
« Reply #121 on: December 22, 2017, 12:02:29 PM »
This is a basic question, but how do you mount the can capacitors to the back panel? In the past I've used clamps, but it seems people are using sockets which look much cleaner. Can anyone link me to the sockets that people are using?

google : metal plate mounting can capacitor

core13

Hello

I have Matching problem, I have 1db difference between units and I need to tweak volume in daw to respect my stéréo image, and it's very annoying .

I thought the problem was from the old pots I used in the filter, but after wiring directly from input transformer to interstage the problem is stil there.
so I think it's the amp
I also swapped the tubes between units and the gain difference remain the same.

I used carbon resistor in the amp so maybe they are not close enough and cause some difference between units?
which resistor I need to look after ?
http://www.recproaudio.com/diy_pro_audio/diy_files/eqp_1a/eqp-1a_schem.jpg


maybe a simpler solution is to add a potentiometer or a Tpad in both units to match level.
I know warm audio did that in their EQP-WA
https://www.gearslutz.com/board/attachments/product-alerts-older-than-2-months/593608d1475765100-warm-audio-eqp-wa-pultec-style-eq-img_2144.jpg

what do you think of it?

Thank you



garp

Do you still have eqp1a and la2a cases ?

jefepeters

Has anyone used the Cinemag CMLI-4x150D input transformer for this project? According to the spec sheet (http://cinemag.biz/line_input/PDF/CMLI-4x150D.pdf), it looks like there's a threaded grommet version that should work with the Sowter adapter plate. Is this correct?

Also, any comments /thoughts on the various  inductors you can use with the project? Unless I'm mistaken, there are at least four options:

MigMa M1958 (https://www.don-audio.com/MigMa-M1958-EQP-1A-Inductor)
Cinemag CML-150T (https://www.don-audio.com/CineMag-CML-150T-transformer)
Vintagewindings EQ-1A (http://vintagewindings.com/products/VintageWindings%20EQ-1A.html)
AML CA-18-VTA1444 (http://www.audiomaintenance.com/acatalog/Inductors.html)

I'm leaning towards the Cinemag, unless anyone has any recommendations otherwise.

Thanks,
Justin


kosi

Yep, this will work. As you are in the USA, I would order everything from Cinemag.
I built 2 Pultecs with Vintage Winding inductors, and I have some problems with ringing. I ordered one AML CA-18-VTA1444, but I had no time to compare it yet.  I also have to say, that I cannot hear the effect of the ringing. The EQs sound fantastic as they are.

My 2cts: Give David from Cinemag a call, he's very nice and can tell you, wether the CMLI-4x150D is good or if you have a better choice. From the technical side, any 600:600 tx will do.

Oh wow. Didn't know Cinemag had an inductor for the Pultec. :o :o  :)

Audio Maintenance has a lead time of approx. 6 weeks from today for the next batch. I heard good things about those, relative to the Vintage Windings unit and the ringing... but wondering how the Cinemag compares to the AudioMaintenance?
"Kind of like going into Safeway at 4 in the morning and chugging a beer in the produce section; been there, done that." - CJ

"We're not making an atomic bomb, just cooking a few electrons." - PRR

i believe the vintage windings inductors had a problem but have  been redone. he talks about it on his site.   I had to send mine back and they gave me some of the newer designed ones instead. Much better!

I think the problem you refer to that seems to have been corrected was reduced high end. Didn't think this was the same thing that I heard was recently (always?) plaguing the VW unit, namely, (slight?) ringing in the high end.

Am I confused, are these the same thing?
"Kind of like going into Safeway at 4 in the morning and chugging a beer in the produce section; been there, done that." - CJ

"We're not making an atomic bomb, just cooking a few electrons." - PRR

Ah, I understand the Cinemag is an E/I (not toroidal) inductor. So, Cinemag is likely "cleaner"/"more linear" but less "mojo" perhaps?...
"Kind of like going into Safeway at 4 in the morning and chugging a beer in the produce section; been there, done that." - CJ

"We're not making an atomic bomb, just cooking a few electrons." - PRR


garp

My two cases finally arrived ! Awesome job here and the overall quality is outstanding , thanks Martin for patience ;) As i had a pair of wonderful radio france output transformers specialy made for the 12au7 (bigger than the peerless but perfectly fitting ) i begun to modify one unit for the mounting of these babies when i discovered that the peerless had windings that i don't have . My trannys are labeled 12au7 for the inputs (two wires) has four output plots ( two tapped together to obtain higher impedence ) and a center tap ... nothing more :( How should i modify the layout to use them ?  Can i use them ? The price of the cinemags clones of the peerless are prohibiting here in europe even with don's help ... do the subtitutes have same problem ? Does a layout exists for such trannys ? Thanks for help ;)

Garp, the output transformer must have the tertiary winding for feedback. To my knowledge, that leaves two choices, Sowter and Cinemag. They are both fine transformers.

I have used the Carnhill inductor and been quite pleased. I had some problems initially with the Vintage Windings inductor, but they have been fixed (see my post about it in this section).

Other important questions are:

- What interstage transformer are you using? If you go with Sowter, spring for the 1475. I used UTC A18 with good results.

- Do you have an audio analyzer to use to tune the Zobel on the interstage to minimize ringing of whatever inductor you’re using?

I’ve not built a unit using all Sowter transformers, the Vintage Windings inductor and the stock interstage Zobel. So I can’t predict performance of that setup. But since no one makes an exact replica of the HS29 (BTW, I wonder why not?), be prepared to adjust the Zobel to suit the transformers and inductor you choose to use. Or just ignore the HF ringing/rise above 26K (if it’s there), since only dogs can hear it anyway.  And it only shows up with boost above 8K, you may never use that. But the only way you’ll see it is with an analyzer.
« Last Edit: May 17, 2018, 11:18:04 PM by AusTex64 »

garp

Thanks for that very clear answer . I made no real choice for the transformers now but i will have to very soon ;) And for the analyser ... i can manage to get one (or do one with a daw orand software).

garp

Ok i just ordered the cinemags output trannys and a pair of don's inductors for a try ... i will go for the sowter interstage also, thanks for advice !

jefepeters

Sowter has two HS-29 replacements listed on their website (http://www.sowter.co.uk/vintage-audio-transformers.php).

Anyone have any opinions on which one to go with? Rainton's BOM lists the 9330 and the Rec Pro Audio kit uses the 1475.

Thanks,
Justin

Justin,

Yes, Sowter has two acceptable substitutes, but neither are an exact match of the Triad HS-29 in inductance and winding impedances. Impedances on HS-29 are 20K ohm/80K ohm. Neither of the Sowter transformers match that. So when one builds an EQP-1A according to the schematic, the Zobel on the interstage was tuned for their inductor and HS-29 transformer. Turns out the inductor likes the HS-29’s low load. If you search my posts about this, I go into detail. But bottom line is there is no interstage transformer commerically produced (to my knowledge) with the EXACT same inductance and impedances of the HS-29. I saw there was a Russian guy offering what he claimed to to be an exact version on eBay, but I haven’t tried it and have heard no other info about it.

Re: rainton's True To The Original PULTEC EQP1-A chassis kit discussion thread
« Reply #136 on: December 30, 2020, 08:30:47 AM »
Hey there,
maybe someone smarter than me knows this.... can i substitute the 20pf/500v cap on the 12ax7 with a 25pf/500v? Or is this too much of a tolerance? Cheers

boji

Re: rainton's True To The Original PULTEC EQP1-A chassis kit discussion thread
« Reply #137 on: December 30, 2020, 05:15:25 PM »
Quote
can i substitute the 20pf/500v cap on the 12ax7 with a 25pf/500v? Or is this too much of a tolerance?
What is the cap's % of accuracy on datasheet?  If it's 20% then a 20pF cap could be anywhere from 16-24pF out of the bag (expect you'll be ok).

Re: rainton's True To The Original PULTEC EQP1-A chassis kit discussion thread
« Reply #138 on: December 31, 2020, 04:56:45 AM »
I think they should be close. Its the original erie ones. What kind of tolerance could i get away with, without compromising anything? Best