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Old 21st April 2011, 05:33 PM   #11
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Default Status update

Hi there,

the project has *not* been abandoned - I just do not have much time besides everyday work...

Right now, the custom-wound mains transformer has arrived:

Click the image to open in full size.

Looks quite good - still have to check if all values are as stated.

Also, I found some time to build one of the B+ filter assemblies for the test setup, consisting of 2x 120F with bleeder resistors. The caps used are 385V rated - I connected two in series because the off-load voltage of the PSU is about 650V.

Click the image to open in full size.

I plan to break the circuit apart into large sub-assemblies to make the building of the final amplifier a little more easy. More filtering for the phase-splitter and the negative rail will be made the same way.

Greetings,
Andreas
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Old 22nd January 2012, 10:14 PM   #12
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Smile Still there *gg*

Hi there,

there wasn't much time for DIY stuff in 2011, working on my PhD kept me from grabbing the soldering iron, financial issues kept me from buying the Lundahl iron for the test setup...

Found some time now to continue with the amp, the negative rail for the pentode CCS below the phase splitter cathodes is up and working:

Click the image to open in full size.

It is a cap input supply being fed from a EZ81 rectifier tube, filtering as follows:

Click the image to open in full size.

Afterwards, the EF184 constant current sink was build, after weeks of fiddling around with LTSpice to find suitable parameters. I used to think that simulating stuff saves time, but it seems to be the other way round...

Schematic:

Click the image to open in full size.

And yes, it works!

Click the image to open in full size.

The small, yellow DMM shows the negative rail voltage, the larger one measures the voltage across a 100 ohms resistor, giving a readout for the programmed current (9.6mA). The CCS is built around the EF184 seen below the middle of the image, the second tube visible to the left side is the EZ81 of the negative rail.

The GZ34 rectifier has been pulled because I don't need the positive rail for the testing, seems safer without having 400V present everywhere... And saves tube life by avoiding all the on/off switching.

Best regards,
Andreas

PS: Edith says that none of my earlier posts mentioned that the positive rail is up and working fine, apart from a slow up/down drift of the DC voltage which is probably due to mains variations.

Last edited by Rundmaus; 22nd January 2012 at 10:23 PM.
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Old 25th January 2012, 01:01 AM   #13
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AW was a firm proponent of using good chokes in the power supply and wasn't particularly bothered about using tube rectifiers. I see you have gone the opposite way.
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Old 25th January 2012, 10:17 AM   #14
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Quote:
Originally Posted by ihear21khz View Post
AW was a firm proponent of using good chokes in the power supply and wasn't particularly bothered about using tube rectifiers. I see you have gone the opposite way.
Hi ihear21khz,

only the negative rail for the current sink is chokeless, due to the low current demands here, it was simpler and smaller with caps and resistors than with chokes. The positive supply for the amp is choke-input

That thing about tube rectifiers is (luckily) no 'religious' question for me. I am aware that the power supplies as well as the current sink would have been much easier with the help of solid state devices. And I do not expect significant performance improvements from keeping solid state stuff out of this project.

It was just an interesting idea for me to build that amp without any semiconductor, although this means that some things are more difficult/bulky/expensive then.

I will report back when the amp is working - which basically means when I have some money to get an output transformer...

Regards,
Andreas
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Old 26th January 2012, 01:11 AM   #15
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Quote:
Originally Posted by Rundmaus View Post
Hi ihear21khz,
I will report back when the amp is working - which basically means when I have some money to get an output transformer...

Regards,
Andreas
You won't regret building this. I have the PP1s and they are great sounding amps. If not for my power hungry speakers, I'd use one or the even better sounding PP2.
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Old 26th January 2012, 10:24 AM   #16
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Following your project too, and also have a plan to build the pp-2 some day. OPT, PT and chokes are inhouse.
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Old 26th January 2012, 12:06 PM   #17
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Quote:
Originally Posted by ihear21khz View Post
You won't regret building this. I have the PP1s and they are great sounding amps. If not for my power hungry speakers, I'd use one or the even better sounding PP2.
Yes, I am really looking forward to listening to that one for the first time - though my test-setup provides only one channel... As stated above, the project is mainly delayed by financial issues - I used to think that the custom-wound power transformer was expensive, but the OPT costs even more, not to mention a set of tubes for one channel....

Regards,
Andreas
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Old 28th January 2012, 07:06 PM   #18
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Default my version of the PP1C

In the year 2000, after finding the original Allen Wright schematic on the Internet (see the schematic at the start of this thread), I made these two monoblock amplifiers.
Vacuum tubes: 2 x Cca (Siemens) and 2 x EL34 (Telefunken).
Transformers were rescued from old amplifiers.
I followed the original schematic.
I used good quality commercial components, no fancy expensive stuff.
I am very satisfied with the result and sound quality of this design, now driving a pair of Klipsch Heresy III speakers.
Best regards, 968driver.
Attached Images
File Type: jpg tubeamp1.jpg (193.7 KB, 158 views)
File Type: jpg tubeamp2.jpg (187.6 KB, 164 views)
File Type: jpg tubeamp3.jpg (301.0 KB, 172 views)
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Old 28th January 2012, 07:23 PM   #19
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Quote:
Originally Posted by 968driver View Post
Transformers were rescued from old amplifiers.
Do I correctly recognize the 1L452 Output transformers as used by carad/artec in their EL34 PP amps?
__________________
Real tubes have top-caps
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Old 28th January 2012, 08:20 PM   #20
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The power transformer is from an Artec EL34 PP stereo amplifier (the one with the horizontal VU meters, they used two of these in the stereo amp, so this is good for two monoblock amps).
The output transformers however, are French Millerioux PP transformers.
The choke on top of the chassis is from an old Hewlett Packard instrument.
All were cleaned and spray painted in Provence blue, inspired by a holiday in the beautiful Provence region of France.
The donnor amplifiers were beyond rescue.
Best regards, 968driver.
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