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I have 2x Maco 300 amps. One is a 7 tube, the other has 6 tubes, with the 5th final tube removed. They both exhibit a strange issue where dead key, after keying for a short time, starts to drop from about 250W down to 100W. After a little while, it climbs back up to regular output and stays...

Yeah. That's a sobering thought of the day.

LMAO, did you read the reviews?

Couldn't you link the pins at the socket for an 8950 for a 2 amp, one shot connection? I guess that wouldn't be a good idea. I don't think the 6lq6 has a dual cathode pin, not per the datasheet anyhow.

That's a good point, nomad. When you explain that, I can kinda visualize it. When I consider how they all failed that way and popped the line fuse in an instant, I'm kinda thinking something is shorted. I really wished I had a schemo, but since it isn't as populated as other, more robust amps...

Can you describe some failures that would take the cathode link out?

Per the datasheet, that link connects the cathode to pin 3. Every one of the finals have a blown cathode to pin3 link, so this is a lost cause. Thank you Shockwave and Nomadradio for your insight. I can't say for sure what caused this condition, but I feel the foiled fuse, and a short somewhere...

That nug performed exactly as specified, it's the prideful human nature that short circuited. The guy acted like he meant to do that. What a mess.

I don't know for sure, but I think these tubes are goners. There is what appears to be a burnt link in every final tube. The trans is good, the cap multiplier checked out and the diodes are rectifying, and then there is this.

That's what I am thinking. I need to check the transformer, rectifying diodes and caps.

I just got a little more info from him, as they never tell all at first. He said the spark could be from a final tube clip that was loose and popped off mid key, and he also said the fuse popped. He put the clip back on the tube and put foil to the fuse, to see if it worked again...Macgyver be...

Thanks guys, I'm going to get him on the phone, try to get more info from him and some better details. I looked over the driver and final chokes and they looked fine, I will discharge any caps and check continuity. The 4 watts in/4 watts out issue seemed to me like the relay isn't switching, but...

I wonder if the squealing mic has a 5 pin connector on a 4 wire cable. When using adapters from 4 pin to 5 pin, a sequel is produced from connecting the ptt ground with the mic audio ground. Worth a look see.

I would think 2 AA batteries in series for 3v, as most button cell batteries for memory are 3v like a cr2025, cr2016, cr2032 etc.

Hi all, I got a 12 tube, 4x8, super scout. I think it's a sos brand, not sure. Looks pretty good under the hood, but doesn't work. Putting 4 watts in gets 4 watts out, regardless of hi/low switch. Both relays make contact when keyed. Was told it was working fine, until a spark was observed...

Yeah, chassis ground is not used for these measurements, board ground is your Huckleberry. Board grounds are capacitively "floating" above the chassis ground, I hope I said that right. I only clip to the chassis when working with the output of the pa stage, everything else gets clipped to the...

Tbh, I can't see that chip getting hot unless you max the volume for a long time, use the wrong impedance external speaker/pa or some fault develops causing it to overheat. Since it doesn't get hot under normal operation, I'd stick the shim to it.

That's shoddy craftsmanship on the manufacturer. You would need to unsolder the tda, possibly replace it if the Leeds are too short. Reducing the thickness of the insulator from thick to thin would exaggerate the tilt. I'd preemptively replace those chips all together, using the thinner Mica...

There is a great source for quality cap kits lurking around the forum, @Klondike Mike has always fixed me up, and it's quicker and likely cheaper getting a kit, as buying quality capacitors sometimes have a minimum order, and many different values. See if he can fix you up. His kits have had all...

Oh, I listened to your growl, I have heard something like that before, just can't remember what it was or where. If it comes to me, I'll let you know.