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Good morning guys....I wanted to follow up on this. This morning I built a new power supply section with a choke as many of you suggested. I'm pleased to report that the choke literally destroyed any trace of power supply hum and now the amp is dead quiet at idle. Thank you for everyone who...

I measured the plate current with a 130 ohm cathode resistor and found it to spot-on at 48ma. Before making any changes to the amp section, I'm going to rewire the power supply with a choke when it arrives. So far, all conditions match the test scenario outlined in the tube manual and I'm eager...

Just to answer a few questions: - 60 uF cap was an experiment. It does help, but to your point, probably has too much inrush for the 5AR4. - All audio circuits ground to a buss bar, which then stars over to a common ground on the chassis. - Power supply ground also stars over the the common...

Thanks for all of the suggestions. I tried elevating the filaments and it made no difference at all. I used off the shelf modern high voltage electrolytics for filter caps. As an experiment, I clipped on a couple of can capacitors and the hum was reduced but I don't know if it's because of the...

Do you mean to add a DC offset? I have not tried that.

Guys, I've been working with audio for years but this one has me stumped. I scratch built a generic EL84 test circuit with a Class-A configuration. All seemed to be going well until I cranked up the bias point to 48ma of plate current, per the datasheet. The gain came way up as expected, but so...

So true, mike 567! I'm going to give it a go because it's too juicy of a challenge to pass up.

I have received a Heathkit AA-100 two years ago which was declared to be unrepairable by 3 different repair technicians. Since I'm always up for a good repair challenge, I thought it would be fun to make video of the repair process and put it out there for your enjoyment! The first video in a...

Hey guys, it's Mike here with pcbgraphix. I designed the power amp PCB kit back in 2016 and a few folks were also asking for new pre-amp boards. I invested a good deal of time and research into designing a new pre but there are two show-stoppers that put an end to it: a) selector switches, b)...

I vote to revitalize. These things sound great when they're well restored.

I blogged the restoration of my AA-100 a couple of years ago. It was a bit of work but the results were worth it. https://aa100restoration.wordpress.com/

Somebody needs to set up a web stream of calibrated WWV audio! Too bad the random latency of the internet would make this Most Un-Accurate as well.

OK so you've amused me. I've been working hard for the past couple of years to help the guys fix their amps and I'd like to reach more people, save more amps from the scrap heap, so what must I do to "subscribe"? I'm already a member of the forum.

Very true! The old circuit boards were terrible. Blah blah blah ....

I'm running a fully restored AA-100 with JBL 4412s...…..Sweeeeeet!

There are now 28 output board kits scattered around the world, including USA, Canada, UK, and Germany. Many thanks to those who have supported this!

I went through the process of fully rebuilding my AA-100 last year. Check out the blog at: https://aa100restoration.wordpress.com/ I had to bypass the MODE selector switch to make it work right, but with full rebuild I found the amp to be sweet! Last year I created a POWER AMP retrofit kit, but...

When I was in high school years ago I had a capacitor blow up under my hand..........Scared the daylights out of me. It was a good lesson in observing voltage ratings!

There's a lot of tube voo-doo out there and I'm always amused when people say that carbon comp resistors which have drifted out of spec and leaky capacitors are somehow sacred. There's a fellow who came over to Gordon's AA-100 thread and chastised us all for taking out "vintage caps". I will...

Moediggz: I see you've resurrected Gordon's old thread. Congratulations on a successful restoration! Once in a while somebody gets lucky and finds an amp that's in great condition and I'm glad it turned out well for you. Most of the rest of us ended up with amps that are/were in horrible...

If you do have a bad pot, check with Mark Opat, a fellow forum member. He has a good stock of NOS parts. Steady hiss though is caused by something else. Carbon comp resistors are notoriously noisy.

What is the nature of the mods you made and what was the purpose for doing them?

Have you tried swapping speakers? I've seen crossover caps get weak and cause problems.

The utility company is supposed to nail the voltage at 120Volts. If it's fluctuating then something is wrong and they need to get out there and fix it. They can put a line monitor on you and tell if there's any problems with their system. I had a neighbor once asked me to help troubleshoot his...