Hello from justinis

[justinis]

Hello, all! My name is Justin and I am an electrical engineer living in DC, working in Arlington. I love vintage and modern audio and visited the Capitol Audiofest 3 out of the last 4 years. This year I visited the DCAudioDIY room for the first time and found out about this forum. I'm so excited it exists and can't wait to jump in!

Past projects:
Restored Akai AP-207, Pioneer SA-6500, Marantz 1060, New Large Advent loudspeakers

Current project:
Building a 50W stereo power amp using a driver board for a Dynaco ST-70, tubes and transformers from a Heathkit AA-100

Future projects:
Marantz 2226B restoration

Current system:
Pioneer SA-6500, New Large Advent loudspeakers, Technics SL-QD33

Last edited by justinis on July 15th, 2016, 11:17 am, edited 1 time in total.

[FerdinandII]

Welcome Justinis,

Those OPT transformers from the Heathkit AA-100 are excellent.
Which driver board are you using?

[justinis]

Thanks! The DIYtube one by Shannon Parks.

[FerdinandII]

From another thread that disappeared......


++++++++++++++++++++++++++++++++++++++
Are you measuring the voltage with a load on the power supply? With no load, the voltage will rise quite a bit. Try a 10k power resistor, or something in that range, so that you are pulling 50mA or so from the PSU. You'll need a big one.... See if the voltage drops down to the specified 445-450 VDC.

Easy fixes are:

Drop a 5R4 rectifier in there.
or
Change it from capacitor-input to choke input.

Have you tried Duncan's PSU simulator? It's great for modeling the impact of component changes.

[justinis]

Sorry, I deleted the thread cause I found an error in my calculations. Just put it back with new values: http://dcaudiodiy.com/phpBB3/viewtopic.php?f=4&t=665

Thanks for the tip! I do indeed have the powers supply loaded; the entire amp is built at this point.

The 5R4 is a good suggestion, thanks. I was trying to avoid it cause I thought the zeners would be cheaper/easier, but now that it's screwing up my neg supply that's probably not true anymore.

Don't understand the capacitor/choke vs choke input. Can you explain?

Thanks!

[FerdinandII]

Sorry, I deleted the thread cause I found an error in my calculations. Just put it back with new values: http://dcaudiodiy.com/phpBB3/viewtopic.php?f=4&t=665

Don't understand the capacitor/choke vs choke input. Can you explain?
Thanks!

You put the choke first, directly downstream of the rectifier, then the filter caps.
It can be Just an "L-C" filter network, or "L-C-L", or "L-C-L-C" (big C at the end).



N.B. For low-level amplifier circuits, the choke input minimizes any high frequency artifacts generated by the rectifier. This is critical for any PSU that uses solid state rectifiers.

[brombo]

If you are running linux (probably for windows also) there are free circuit analysis (simulation) tools available. Tubes can be modeled as linear (small signal transconductance model) or non-linear (non-linear voltage controlled current sources). There are also digital design and simulation tools and pcb design tools available.

[brombo]

Here is link to tube models in SPICE circuit simulation code -

http://www.normankoren.com/Audio/Tubemo ... ticle.html

[FerdinandII]

Duncan's PSU Designer is the best, IMHO.....

http://www.duncanamps.com/psud2/download.html

[brombo]

I was thinking more of simulating the entire amplifier.