new sunn amp day!

[loudthud]

The power transformer is supposed to be 28-2360 (confirmed) and the output transformer should be 28-1360 (too hard to read at that angle). So there is no question in my mind that it's a 60W transformer set.

The 190L amps were older chassis' with a big sticker on the front covering the old name. This could be one of those amps with the sticker removed.

[biltmore]

The 190L amps were older chassis' with a big sticker on the front covering the old name. This could be one of those amps with the sticker removed.

Whoa. I never knew about that. I just did some searching and ran across this post, which you lovingly provided the schematic for the 190L:

http://sunn.ampage.org/sdp/index.php/topic,4772.0.html

I can't read schematics at all ... but the Sentura I certainly looks a hell of a lot like the 190L:

http://sunn.ampage.org/site/museum/190l/

I think you may have just solved the mystery about this amp! That being said, is the 190L supposed to get growly early? Or does it look like it might just be the 6AN8 that's causing the early breakup? We'll probably take the amp down to Portland Custom Shop to get it checked out. Can you corroborate my friends comments about the amp, so that I can give PCS a heads up about the amp? We'll be sure to give them the 190L schematic since you found out what the amp is.

A few things standout:
 - Yay, replaced electrolytics! ... except on the PCB. The two big guys and the four blue ones are forty years old. They will not be in their best shape!
 - DEATH CAP! The capacitor from the switch to the chassis is bad. Cut it out. (bottom left corner of this pic http://i64.photobucket.com/albums/h179/dead_red_eyes/Sentura%20I/DSCN3761.jpg)
 - Shoddy 3 prong install. The previous owner has added a 3 prong power lead, but soldered the earth lead to the chassis. Lame. It should be soldered to a lug then bolted to the chassis with a locking washer between it and the nut. Also, the earth lead should be longer than the live and neutral leads so that if the power cord gets ripped out, it will cop the strain last and hopefully remain connected, preventing the chassis from going live.
 - Unbalanced high voltage capacitor stack. The two absurdly large blue sprague caps are in series to safely handle the voltage present at the first B+ node. However, it is standard practice to put a large value resistor across each of these to ensure the voltage seen by each is exactly half of the entire voltage present. Otherwise one can get a voltage above its max rating and meet an early death. A 220K/270K/330K 1W (or higher) resistor from the + to the - of each of those two big caps will act as a voltage divider and perform the aforementioned task. What I'm describing can be seen in the power supply for the hiwatt DR103 - http://hiwatt.org/Schematics/DR_100wPS.gif

Can't thank you enough for the help loudthud!!! Your services are invaluable my friend. I don't know what any of us would do if we didn't have you guys around to help us out. It's stuff like this that really makes me want to see the site being updated with more schematics, new additions and higher quality pictures in the musuem, and maybe even an extensive bio section. If this site went away one day, I think I can safely say that a lot of us would be left in the dark ... and that would certainly suck.

[pickinatit]

That  2 X 12  cabinet looks just like the cabinet that I got with my Solarus fourty odd yrs. ago.  Is that cabinet "open back" ?  You hardly ever see one of them up for sale on  e-bay or craigslist.  I have Hellatones (celestions) in mine. One vintage G30 &  one G12h30  and I love the way they sound,  but that's a personal preference.  One of these days I'll get the Sunn speakers re-coned.

[biltmore]

It's a closed back cabinet. It's definitely the first 2x12" Sunn cab that I've ever seen. If it didn't have the same grill cloth, tolex, and name badge as the Sentura I / 190L .... I would think it wasn't a Sunn cabinet.

I'll be sure to get some more in depth photos of the cabinet tonight for everyone to check out.

[loudthud]

Is that 9-14-70 on the "Tested" sticker? That seems a little early to be a 190L. There is no original date on the 190L schematic but rev A looks like it was added 10-9-71. Your amp has the tube rectifier and the older Vibrato circuit board so it might have been a prototype of the 190L which had a solid state rectifier and a different Vibrato board. From the Sunn Catalog Thread, it looks like the Sentura (I and II) name was dropped in 1970 as were all the 40W amps.

[biltmore]

I believe it says 9-14-70 on the tested sticker and there's another on the top of the chassis, but there's dirt on it and I can't make out what it says. The 0 really isn't connected all the way, and at first I thought it said 9-14-76 but that can't be right. There's a number on the side of the chassis in red pen that says "#402", but I haven't the faintest idea as to what that's all about.

It would certainly be crazy if this is a rare prototype. Do you have any other ideas that we should check into to see what this amp really is? Check the numbers on the potentiometers by chance?

[sundhy]

This is a Sentura II with a Sentura I faceplate.  Hope it wasn't a factory error!

Conrad sundholm

[biltmore]

Thanks for checking out the amp Conrad! Really nice of you. It's nice to know what it is now.

[Soundmasterg]

This is a Sentura II with a Sentura I faceplate.  Hope it wasn't a factory error!

Conrad sundholm

Well if it was, I guess no one noticed until now when you did Conrad.

Greg