Recent Posts

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21
Q & A / Re: Recently Repaired 1968 Blowing Fuses... What to do?
« Last post by Isaac on January 20, 2025, 11:09:35 am »
When I was a technician in the Navy, we were allowed to replace a blown fuse once. If it blew again, troubleshooting began.

I don't recommend this in your case, though. The burnt resistor indicates an existing problem. The fuse blew, preventing it from getting worse. Putting another fuse in might allow the problem to get worse.

LOUDTHUD has made some good suggestions, if you're inclined to tackle the problem yourself. Otherwise, I'd take it back to the technician and tell him, "You missed something."
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Q & A / Re: Sunn 215 JBL vs. 215 transducer speakers quality difference
« Last post by Isaac on January 20, 2025, 11:00:53 am »
I wouldn't say that. The volume control on the 200S amplifier is able to set an appropriate level.

In my opinion, the JBL speakers simply sound better, and are always the better option, if available.
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General Discussion / Re: Repro Sunn Products
« Last post by Soundmasterg on January 18, 2025, 04:05:15 pm »
I too saw the Sunn offerings, which is great. I was thinking about ordering some for myself. The first gen grille cloth should be the same as what came on my very early 2000S without the bass boost switch right? I think it is the same stuff that AIMS used for their amps too. I happen to have an early 70's AIMS amp that I need to restore. I always liked Sunn's tolex....it was thicker and more robust than what Fender used in the era.

Greg
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General Discussion / Re: Repro Sunn Products
« Last post by loudthud on January 17, 2025, 06:21:31 pm »
I'd like to see someone who makes reproduction head shells for 40 and 60 Watt heads. I think they are identical for 40 and 60s, the 120W heads are just longer.
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General Discussion / Repro Sunn Products
« Last post by Ryan Phelps on January 17, 2025, 05:48:39 pm »
Dear Sunn Bretheren,

I received notice yesterday from AEC (Antique Electronic Supply) that they now carry several several replacement parts for Sunn amps.
This includes Sunn tolex and 1st generation Sunn grille cloth ...both unobtanium for decades. I suspect that these parts are being reproduced by the new owners of Sunn.

Note that the numbered Rogan 155 knobs offered by AEC are not exactly correct for the original 1960's - 1970's Sunn tube amps. The font used on these knobs are "square-sholdered" .... correct for old Music Man amps, but not Sunn.

Fortunately for me, I have a stash of Fender-era Sunn tolex (purchased from Conrad Sundholm a decade ago), 2nd generation grille cloth (purchased from the original manufacturer) and the correct 155 Rogan knobs (with the "round-sholdered" numbers).

I hope this info is of use!

No affiliation with Sunn. Just an old Sunn collector / amp tech.
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Q & A / Re: Recently Repaired 1968 Blowing Fuses... What to do?
« Last post by loudthud on January 17, 2025, 01:22:01 am »
Do you have a DVM with a DC Volts range of 500V or higher and a diode check function ?
27
Q & A / Re: Recently Repaired 1968 Blowing Fuses... What to do?
« Last post by loudthud on January 16, 2025, 09:33:38 pm »
Is the burned resistor on the terminal strip circled in red on this pic ? That's the bias supply. When the bias supply fails, the power tubes draw maximum current until something breaks, hopefully the fuse. Question is, what made it fail ? In normal operation it doesn't receive much stress.

Is there a red wire with a yellow stripe coming out of the power transformer ? I didn't see it in your photos.

28
Q & A / Re: Recently Repaired 1968 Blowing Fuses... What to do?
« Last post by loudthud on January 16, 2025, 09:19:35 pm »
A "Light Bulb Limiter" will keep fuses from blowing and assist in troubleshooting. Not likely to be a bad transformer. Lets try to figure out what caused the fuse to blow.

This should be the correct schematic for your amp. If your amp has a 7199 tube, it's the correct one. If your amp has a 6AN8, it's the 60W version like the 200S. Is there a date or inspection sticker anywhere on the amp ?

A chronic problem with these amps is the way terminal strips are grounded to the chassis. The pop rivets can get loose over time. I recommend that you get a large soldering iron and solder any terminal strip that is used for a ground to the chassis. The way those new caps are grounded is likely the source of any buzz, but you should fix the fuse blowing first.

As you can see from the schematic, the amp came with EL34s. 6L6GC or 5881 are not as strong in this application. Can you get your old GZ34 back from the people that replaced it. It will probably last longer than any currently manufactured replacement.

Keywords Sonaro schematic

Link to Light Bulb Limiter: https://www.ssguitar.com/index.php?topic=2093.0 You need old style incandescent light bulbs to make is work right.

29
Q & A / Recently Repaired 1968 Blowing Fuses... What to do?
« Last post by sntz2 on January 16, 2025, 09:36:34 am »
Hey y'all,

Recently I got my Sunn Sonaro repaired. I got it for a steal in a beat to hell state:
  • mismatched 6L6 tubes, no idea about biasing
  • ripped off a combo and in a custom too-short enclosure for modern EL34s or 6L6s
  • ungrounded plug and death cap, tons of buzz

So I got it repaired and worked w the tech to settle on this:
  • new JJ 5881 tubes, rebias, and a new JJ GZ34
  • new power section caps, bypass the multicap w regular caps
  • new plug, get rid of the death cap
  • replaced some burnt resistor in the power section

Overall, was pretty happy with the work. I understand circuits, but am not experienced with higher voltage power sections so I stick to pedals and bring amps to techs.
I try it in and the shop and it works great. I take it home, it doesn't want to turn on. Okay. I wait one day, try again, works fine.

I play it for about a month and yesterday I get the same thing, except waiting a day does nothing.
I check the fuse and it's blown. Not super burnt or anything, but no continuity with a multimeter. Visibly the wire is broken.
I ask the tech what they think and they think it could be faulty switch wiring. Not sure how that relates to the fuse blowing, but also unsure why the fuse suddenly blew after working (if it was bias or something I'd expect that it'd blow everyday I switch it off standby, right away)

What do y'all think? Any harm in trying new fuses? Does it seem like it could be a bad transformer?
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Q & A / Re: Sunn 215 JBL vs. 215 transducer speakers quality difference
« Last post by Ganoderma lucidum on January 11, 2025, 10:26:40 am »
Thanks for that info.

Regarding volume, would you say the transducers are more appropriate for a lower volume setting then, such as in a home setting?
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