Slowly making some progress on the power supply. I spent nearly two days in getting the chassis done and still not finished.
I ended up fitting both LT and HT supplies in the same chassis. HT Chokes are mounted on top of the plate and HT transformer and filament supply transformers are mounted inside at 90 degrees. Also fitted the two raw filament supply boards and the Salas regulator.
It took me ages to cut the top plate to fit the three oil caps, hard work.
Finally got a nice Telefunken AZ1 mesh at a reasonable price on e-Bay. See the picture.
Still need to fit bottom plate and wire multipole connector.
I'm getting really close now!
Cheers,
Ale
I ended up fitting both LT and HT supplies in the same chassis. HT Chokes are mounted on top of the plate and HT transformer and filament supply transformers are mounted inside at 90 degrees. Also fitted the two raw filament supply boards and the Salas regulator.
It took me ages to cut the top plate to fit the three oil caps, hard work.
Finally got a nice Telefunken AZ1 mesh at a reasonable price on e-Bay. See the picture.
Still need to fit bottom plate and wire multipole connector.
I'm getting really close now!
Cheers,
Ale
Attachments
Finally finished the preamp today. The results have clearly exceeded my expectations when I first started the project, albeit I was caught up by the popularity of it. I hooked up the preamp to my 45 SE and tried "Take Five" from Dave Brubeck on vinyl, which is one of my favorite songs for listening tests. The improvement on the bass response is remarkable and it gives a clearer and rounded soft sound. Tried a couple of times bypassing it and putting back again the preamp. Had clearly improved my systems, that is the final verdict.
Still need to do some proper measures. There is no audible trace of hum apart from when the HT power supply is switched off (previously discussed on this thread). I did a quick THD and frequency response which I will upload later. The 60Hz and 120Hz peaks are well below -85dB and THD is 0.04% for a 1Vrms input signal at 1kHz (valves were randomly selected so could be even better than this if I pick up the best ones I have).
Will do more tests later, but wanted to post my first impressions.
I highly encourage everyone to start the journey of this wonderful preamp project. Having a modular preamp setup, I will tests 10Y, 01A, 112a, 30/VT-67 and more valves to see what I end up liking more.
My special thanks to Andy Evans, Rod Coleman and Thomas for the invaluable help and support all along.
Cheers,
Ale
Still need to do some proper measures. There is no audible trace of hum apart from when the HT power supply is switched off (previously discussed on this thread). I did a quick THD and frequency response which I will upload later. The 60Hz and 120Hz peaks are well below -85dB and THD is 0.04% for a 1Vrms input signal at 1kHz (valves were randomly selected so could be even better than this if I pick up the best ones I have).
Will do more tests later, but wanted to post my first impressions.
I highly encourage everyone to start the journey of this wonderful preamp project. Having a modular preamp setup, I will tests 10Y, 01A, 112a, 30/VT-67 and more valves to see what I end up liking more.
My special thanks to Andy Evans, Rod Coleman and Thomas for the invaluable help and support all along.
Cheers,
Ale
Attachments
Oh man, I'm listening now to Sonny Rollins and discovering a bass that was hidden in my amplifier!
Still using a simple pair of national union 26...
Thanks Thomas,
What can I say, the LL1660s, the oil caps and the power transformer are superb. Thanks for that!
Hi Regal,
No I haven't. I tried briefly a couple of old 226 and one was a bit microphonic. Then stayed with the national union 26 pair I had at hand. I have many 26 valves so will test and report.
Cheers,
Ale
An externally hosted image should be here but it was not working when we last tested it.
Testing some valves from a selection of about 40 26s and 226/336s from various brands. All classified by their THD ranging from 0.02% to 0.2%.
So far I preferred the Cunningham CX-326 (clearer tone, better mids) and then the Sylvania 26.
You need to buy in the USA for 26 tubes. Always plenty of Cunningham on ebay
EXCELLENT NEW TESTED CUNNINGHAM GLOBE CX-326 TUBE NOS+ TESTED 326 26 TYPE TUBE | eBay
Cunningham CX-326 tube - engraved base ## | eBay
Vintage/Antique Globe Shaped Radio Tube Cunningham CX- 326 Engraved Base | eBay
EXCELLENT NEW TESTED CUNNINGHAM GLOBE CX-326 TUBE NOS+ TESTED 326 26 TYPE TUBE | eBay
Cunningham CX-326 tube - engraved base ## | eBay
Vintage/Antique Globe Shaped Radio Tube Cunningham CX- 326 Engraved Base | eBay
CeCo globes from Canada are quite nice as well if you can find them - amongst the best sounding with the Sylvanias and Cunningham CX-326 referenced earlier - noting that Cunninghams were made by RCA, RCA ones having the same general construction will also sound quite good. IMHO hard to find a bad sounding 26..
On eBay watch out for tubes that are advertised as used and have marginal transconductance (if posted) as they will often be quite noisy in addition to just not sounding good. All of my eBay scores incidentally have been fine, but some I pulled from an old Radiola 17 were not too good unfortunately.
On eBay watch out for tubes that are advertised as used and have marginal transconductance (if posted) as they will often be quite noisy in addition to just not sounding good. All of my eBay scores incidentally have been fine, but some I pulled from an old Radiola 17 were not too good unfortunately.