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Post subject: New find - Sunn Spectrum II
Posted: Sun Mar 16, 2014 11:43 am
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I just picked up this Spectrum II (the external pic is from a web search - I took it apart before taking pics) and thought I'd have a real mess on my hands when I pulled the chassis out. It's got a bad re-cover with the wrong vinyl and has been sitting in a guy's garage for twenty years according to him. The jacks and sockets are corroded but the inside of the chassis is spotless. Sparse compared to my Sentura II but absolutely spotless.

There isn't a date written on the chassis but the pots are dated the 34th week of 1969 and the initials "CAD" and an "OK KJ" are written in red pencil.

It's got a very old GEC KT88 and a Sylvania 6550, both Coke-bottle types. A GE 5U4GB, a Sylvania 12AX7A and a 6AN8A round out the tubes. It looks like it has never been touched inside.

Is there a source for the original style Tolex or at least something close?

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Post subject: Re: New find - Sunn Spectrum II
Posted: Sun Mar 16, 2014 2:49 pm
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Congrats on a great find.

I would definitely go through the amp just as I would with any vintage Fender. The specified rectifier is a GZ34 so that's the first thing that should happen. A matched set of 6550's should follow suit. It's likely that the amp retains its original filter stage so a new cap can is probably also in order. Don't forget to inspect the power-rail resistors and replace any that look (or measure) wonky. Here's a pretty decent set of bottles for that amp that won't require congressional authorization or bust the Federal Reserve......

http://www.ebay.com/itm/SUNN-Spectrum-I ... 0716954661

You can find the correct covering for the cab on Ebay as well.

Arjay

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Post subject: Re: New find - Sunn Spectrum II
Posted: Sun Mar 16, 2014 4:31 pm
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Yeah, the schematic says GZ34 but the tube chart (I know, don't believe the tube charts) says 5AR4.

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Post subject: Re: New find - Sunn Spectrum II
Posted: Sun Mar 16, 2014 4:44 pm
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A 5AR4 is a GZ34.

Arjay

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Post subject: Re: New find - Sunn Spectrum II
Posted: Sun Mar 16, 2014 5:51 pm
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Yeah, I'm aware of that. I thought you meant it had to be a GZ34 specifically which is why I was confused.

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Post subject: Re: New find - Sunn Spectrum II
Posted: Sun Mar 16, 2014 6:21 pm
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What it doesn't need to be is a 5U4GB.

Arjay

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Post subject: Re: New find - Sunn Spectrum II
Posted: Sun Mar 16, 2014 6:53 pm
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Ok, I just read it's not a good choice as it can shorten the life of the other tubes, is that why?

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Post subject: Re: New find - Sunn Spectrum II
Posted: Sun Mar 16, 2014 10:21 pm
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The 5U4GB's heater requires 30% more current than that of the specified GZ34/5AR4 -- I'd be more concerned about damaging a vintage-and-near-irreplaceable power transformer.

Arjay

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Post subject: Re: New find - Sunn Spectrum II
Posted: Mon Mar 17, 2014 7:09 am
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Gotcha. I appreciate that info!

Funny thing is, I almost pulled up the tube data sheets on them last night to compare. :)

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Post subject: Re: New find - Sunn Spectrum II
Posted: Mon Mar 17, 2014 8:36 am
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If you're serious about tubes and their operating characteristics, pick up a copy of the RCA Receiving Tube Manual. You can often find them on Amazon or Ebay for fifteen bucks or less.

Arjay

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Post subject: Re: New find - Sunn Spectrum II
Posted: Mon Mar 17, 2014 3:10 pm
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Original Tolex material is now NLA, but there are several sources for very good replacement material.

Vibroworld offers 'new' and 'old' grain 'Tolex.

MojoTone also offers replacement material which looks more like the vintage stuff.

cheers!

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Post subject: Re: New find - Sunn Spectrum II
Posted: Mon Mar 17, 2014 3:26 pm
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Lightnin MN wrote:
Original Tolex material is now NLA, but there are several sources for very good replacement material.

Vibroworld offers 'new' and 'old' grain 'Tolex.

MojoTone also offers replacement material which looks more like the vintage stuff.


None of those coverings from either vendor is correct for a vintage Sunn amp.

This is the appropriate material......

http://www.ebay.com/itm/NEW-Genuine-Fen ... 2ecf737f59

Arjay

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Post subject: Re: New find - Sunn Spectrum II
Posted: Fri Mar 28, 2014 7:46 pm
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Well it lives and it sounds pretty darned good! It's amazing what a fresh set of tubes and caps will do for something that looked so bad to start with. Oh and it's LOUD! Very clean, not quite sparkling but still not an unpleasant tone. I am going to replace the pots and jacks, no sense in taking a chance on iffy parts.

The cabinet from my Sentura II is identical, I think I'm going to use that instead and worry about recovering this one when I get the Sentura fixed. That'll be a while I think.

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Post subject: Re: New find - Sunn Spectrum II
Posted: Fri Mar 28, 2014 8:09 pm
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The Sunn's were beautiful bass platforms -- ample amounts of both loud and clean. The 60-watt chassis was standardized to fit the 24" enclosure: thus it shouldn't be any issue to swap head cabinets while the Sentura awaits repair and reconditioning. You might try merely cleaning the pots, switches, and jacks with some De-Oxit rather than replacing them wholesale, and perhaps needlessly.

Have you got a 200S or Sceptre cab to mate your head to......?

8)

Rawk on!

Arjay

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Post subject: Re: New find - Sunn Spectrum II
Posted: Mon Mar 31, 2014 8:27 am
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I have a 2x15" cabinet that's in really good shape aside from a 1/2" hold in the grille cloth. I need to look up the speakers, there weren't any when I got it and I think I have one CTS and possibly an Eminence for it.

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