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You are both right - for me, it's a matter of best practice, just in case a signal source is there. Under quiescent conditions and no stability issues no harm should be done. It's kind of belt and suspenders thing. Many of the ones I worked on had a tuner (or it was actually a radio). Even...

Just had another look at that schematic. I mis-read the cathode voltage for the EL34s (pin 8 to ground). It should be +0.3VDC (not 3vdc). That'll be a function of the Output Balance control (R2) and the Bias control (R3). The grid voltage should be -35VDC. On these old amps the coupling...

Is that the one?

Acrosound Ultra-Linear II Here's the link & the schematic is attached.

Ha ha. That should suffice.

Looking at the photo it looks like it has been updated sometime in the past - the perf board doesn't look original. If this is the Acrosound Model Ultra-Linear II, then the cathode resistors are R17 & R20 using the schematic from Radio Museum. Output tubes are EL34s and the cathode voltage...

Tube amps will generally survive momentary (short term measured in seconds if not minutes) disconnects of the output load, but it stress the output transformers and output tubes. With no audio input the load resistors need not be high wattage. My recommendation would be to check the output...

Definitely do not turn them on without a load on the output transformers.

I have both a Sencore SG165 and a Leader LSG-231 (the Leader 3214 in the previous reply is newer). Both are ok for older analog tuners, but both need to be gone over with a fine tooth comb to ensure they are working to spec. I wouldn't use them to align newer tuners except to check for gross...

Excellent. There are apps for the iphone and Android.

Restored the Marantz about 6-8 years ago. Also have a Yamaha CT-7000 tuner. BTW, FM is the way I stream most of my music around the house. Or actually I stream music to a FM transmitter that I tune my FM receivers to.

A couple more photos of the amp...

There were a bunch of threads concerning this power supply back in the 05 - 06 years where folks were having problems with stability. No one ever mentioned (or I missed it - could be true too) the critical nature of the filter caps. I spent a lot of time investigating the PI filter network...

So almost 2 years ago I was scouting around for something to build - something really different other than a restoration. I began looking into a bunch of old electronics magazines (found here: World Radio History) and eventually came upon this: K6 Amplifier. What intrigued me about this was...

Jim will get my attention - my mother used James when I was in trouble. Blue Crab since we live part of the year in the Chesapeake watershed - Crab cakes and Old Bay. We'll head for Florida sunshine after Christmas - getting tired of wearing 40lbs of clothing and it's not even really cold here...

I do like the Expander on particular types of music - the Who's "Won't get fooled again" comes to mind - Roger Daltrey's primal scream . I'm sure in a live concert they had the amps cranked to max. When I play it for my kids, I often ride the volume control to punch up the dynamic range at the...

Agree. The routing of these signals will be unique to the PL4000 and I suspect cutting all traces and using shielded wire to route the signals would correct the issue. Interesting that after the emitter follower the signal is reduced by 12.5dB (voltage divider made with by a 7.5k & 24k...

So, just to be clear, as far as I can tell this increase in THD at higher frequencies is not due to the Autocorrelator boards themselves. It occurs whether or not those boards are installed. I believe it is solely due to the way the signal is routed on the front panel to the motherboard to the...

I acquired an HP 8903B Audio Analyzer a year or two ago, but hadn't really used it. Initially I used it to check a Dynaco PAT4 I bought cheaply off EBay. This PAT4 has a nasty scar and bend in its faceplate. I bought it with the thought of using it to do some experimentation, but that's a...

160vdc is the max you can get from 120vac (120 x 1.414 minus some drop across the diodes) without using a transformer or voltage doubler. With regards to whether or not it needs to see a load for relevant measurements, I would think not, but a light load of say 5k would allow the power supply...