Heath AD-19
- TC Chris
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Heath AD-19
About 20 years ago, maybe a few more, I found a Heath AD-19 "Stereo Cadenza" (i.e., a console) sitting at curbside. It was missing speakers and the speaker-compartment backs. I extracted the chassis and changer from it and stood it on end in the general-storage bay of my garage. The chassis has been sitting in my shop gathering dust. A few years back I bought woofers and tweeters for it. When I got it, one channel was mostly out.
That means that when I connect speakers and turn it on, the L channel is weak and crunchy. It only makes sound, and none too good, with the volume cranked up.
I tried that again tonight since the weather was unsuited to sailing. The speakers are some little JBL 62T ones that sound pretty good for little guys. The R channel? Very nice indeed. L channel is the same as before--only audible at cranked-up levels, and then it's poor quality.
It's possible that the output transistors were damaged (speaker wiring was loose when I got it). They are germaniums-- a 2N148 and TA2577A pair. It took some searching to figure that out. The schematic I have is low-rs and the numbers are not clear. I have not tried to find cross-ref. numbers yet. Or it could be that the driver is damaged, or the electrolytic caps are caput. The solution will be to take my audio signal tracer to it, but the problem is that the chassis is laid out to fit the console and is formed around a gap for the changer, so seeing what goes where is a bit of a challenge.
So my first question is, has anybody else heard a P-P transistor amp with bad germanium OP transistors, ones that still work a little? Or are they either/or devices?
Chris Campbell
That means that when I connect speakers and turn it on, the L channel is weak and crunchy. It only makes sound, and none too good, with the volume cranked up.
I tried that again tonight since the weather was unsuited to sailing. The speakers are some little JBL 62T ones that sound pretty good for little guys. The R channel? Very nice indeed. L channel is the same as before--only audible at cranked-up levels, and then it's poor quality.
It's possible that the output transistors were damaged (speaker wiring was loose when I got it). They are germaniums-- a 2N148 and TA2577A pair. It took some searching to figure that out. The schematic I have is low-rs and the numbers are not clear. I have not tried to find cross-ref. numbers yet. Or it could be that the driver is damaged, or the electrolytic caps are caput. The solution will be to take my audio signal tracer to it, but the problem is that the chassis is laid out to fit the console and is formed around a gap for the changer, so seeing what goes where is a bit of a challenge.
So my first question is, has anybody else heard a P-P transistor amp with bad germanium OP transistors, ones that still work a little? Or are they either/or devices?
Chris Campbell
- electra225
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Re: Heath AD-19
I might suggest that you start by cleaning the controls just in case they are dirty. You didn't mention them. Check for corroded connections. Have you swapped speakers channel to channel? Start with the simple stuff, things easily overlooked or taken for granted then go from there. Good luck and keep us informed on your progress.
Why is the weather not good for sailing?

Why is the weather not good for sailing?


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- TC Chris
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Re: Heath AD-19
I did twirl and wiggle the controls--no positive effect. Speakers should be good--they have worked elsewhere. Same problem with different speakers before.
Chris Campbell
Chris Campbell
- electra225
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Re: Heath AD-19
Do you see any bulged capacitors? Solid state stuff is full of e-caps.
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- Motorola minion
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Re: Heath AD-19
Transistors can fail partially and if one in a push-pull pair does short or open, this is exactly what you get. Check voltages and if anything is off, remove the transistor to check it.
A signal tracer can be used to see in early stages, where the sound gets distorted as you go toward the outputs.
Open electrolytic caps (higher values for SS 1-50mf) can be checked by jumping one across it.
A signal tracer can be used to see in early stages, where the sound gets distorted as you go toward the outputs.
Open electrolytic caps (higher values for SS 1-50mf) can be checked by jumping one across it.
- electra225
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Re: Heath AD-19
Shango used to check electrolytics by using them as an audio coupling capacitor. He hasn't done that in awhile in his videos. He used to say it was foolproof. You really need an ESR tester if you are going to get deep into solid state audio. Can you safely use a signal tracer in the output section of a solid state amp?
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- TC Chris
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Re: Heath AD-19
The issue is that this chassis is designed for a console, so the electronics are hidden all over the place under sheet metal and behind transformers. And of course the suspect channel is the one that it's impossible to get at.Motorola minion wrote: ↑Tue Jul 23, 2024 6:39 pm Transistors can fail partially and if one in a push-pull pair does short or open, this is exactly what you get. Check voltages and if anything is off, remove the transistor to check it.
Open electrolytic caps (higher values for SS 1-50mf) can be checked by jumping one across it.
Chris Campbell
- hermitcrab
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Re: Heath AD-19
first if speakers are capacity coupled start there and work back , if the speaker wires did short then the outputs could be shorted but as stated a VOM will tell you ... I might have some of those outputs ...
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Re: Heath AD-19
It's sitting out in the shop with its fuzzy schematic. I'll check it when go out to lock up.
Chris C.
Chris C.
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Re: Heath AD-19
I am trying to remember if this AD-19 console had a repurposed stand-alone Heath receiver as its electronic guts--like maybe the AR-14 or for the amp section, the AA-14?
Chris Campbell
Chris Campbell
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Re: Heath AD-19
OK, I got out the little Radio Shack "transistor checker" and discovered crud in the battery compartment (will I ever learn?). A little vinegar took care of that and I went out to the shop to check the outputs. One channel--AOK. The other channel--the PNP, TA2577A, was dead per the checker. The NPN, a 2N2148, tested as functional. I am inclined to replace both in that channel.
Circuit descriptions tell me that the NPN is germanium and the PNP is silicon. So the one that's supposed to be more durable is defunct. Worse, I'm not having much luck finding them online.
There are several offers of 2N2148 for sale. Most are a bit pricey, but since everything else is working on this device, I may forge ahead.
Any suggestions for sources for obsolete transistors?
Chris Campbell
Circuit descriptions tell me that the NPN is germanium and the PNP is silicon. So the one that's supposed to be more durable is defunct. Worse, I'm not having much luck finding them online.
There are several offers of 2N2148 for sale. Most are a bit pricey, but since everything else is working on this device, I may forge ahead.
Any suggestions for sources for obsolete transistors?
Chris Campbell
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