Solarus Tubes

[Jagermonster]

Hi, all. Just bought a Sunn Solarus, which appears to be in great condition. However, the markings on the tubes are worn off. I know it has two 6550s and a weird rectifier tube. But I have three tubes, all of which appear to be 12ax7s. Doesn't the Solarus take a 12ay7 or something? I can't tell which tubes go where. There are a pair of sockets toward the front of the chassis and there's a single socket in the middle. What goes where? Thanks in advance. I'm glad to finally have a Sunn so I can get the most out of this awesome forum.

[mckinnon audio]

   Hi there,if it has a rectifier tube it probably shouldn't have 6550's in it unless it's been modded.Mine has 1-GZ 34, 2- EL 34's,(or 6CA7's),1- 12AX7,1- 12AU7 and 1- 7199 phase inverter for tubes.Looking at the back of the amp from right to left should be 12AX7,12AU7,7199,two output tubes,rectifier.Hope this is of some help,Mel.

[Jagermonster]

The date on the inside of the chassis says 1970. Isn't that era appropriate for 6550s? Is there any easy way to tell if its been modded or does that just mean is definitely shouldn't have 6550s in it?

[mckinnon audio]

  Hi there,the only reason I said that is that I have a Solarus with 6550's and it has a solid state,(diodes) rectifier.Maybe they made a model with both a tube rect. and 6550's,I don't know but I'm sure someone on here does.I think the date on mine with the 6550's is 1973,Mel.

[EdBass]

I know that Sunn changed from British KT88's to Domestic 6550's in mid 1969 citing superior performance and "supply issues", but I suspect it was actually financially motivated. I thought that the switch was made to  SS rectifiers at around the same time.
I have a "for sure" unmolested stock 1970 Sceptre with a SS rectifier and Tung Sol 6550's. 

[Soundmasterg]

I've got a 9/1970 Sonic 1 that was identical to a 200S, and the faceplate was all worn off, so I made it into a 200s with new labels. It has a tube rectifier stock, though I changed to larger caps and a Weber Copper Cap rectifier. On the earlier stuff they were using Dynaco transformers, and at some point they changed to Schumacher transformers, and I think that is when they made the KT88 to 6550 switch. I'll have to see if Conrad remembers when the change was and what not. My Sonic 1/200S has the Schumacher transformers, and the voltages are higher and they don't sound as good as the Dynaco ones IMO. Even modding the dropping resistors to get in the same voltage range for the phase inverter and preamp doesn't get the good sound of the Dynaco ones though it gets some of the way there.

Greg

[Jagermonster]

This is why I love this forum. I had a look at the tubes last night, and the 6550s look old enough to be originals.

[Jagermonster]

Been doing a little research. From what I can tell, it seems that Sunn included 7199 phase inverters tubes with amps equipped with EL34s. For a time, 6550 equipped amps had 6A8N PI tubes before switching to solid state rectifiers.

The only problem is, my phase inverter tube doesn't have any markings on it. Is there any way to find out what kind of tube it is, and therefore figure out what kind of power tubes it had originally?

Thanks in advance, just trying to get to the bottom of this, even though the amp is probably just going to the tech soon anyway.

[mckinnon audio]

  Hi there,look at the output and power tranny's,they have a # on the side of them that you can use to determine their size.Just a note,even though they are similar tubes,(triode/pentode),you can't put a 6AN8A in place of a 7199 unless you rewire the socket,good luck,Mel.

[loudthud]

An easy way to tell the difference between the 40W and 60W amps is the height of the transformers. The power and output transformers in the 40W amps are roughly 3 1/2 to 4 inches high and in the 60W amps they are 4 3/8 to 4 3/4 inches high.

Another way is to measure resistances at the 9 pin phase inverter tube socket. In the 40W (7199), pin 8 will measure 47K ohms to ground. In the 60W (6AN8), pin 3 will measure 47K ohms to ground.

[Jagermonster]

thanks a ton, guys. lots of helpful info here, as usual. if anyone is curious, the amp in the link below is set up exactly like mine. the date is within a couple weeks as well.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290375104293&ssPageName=ADME:X:RTQ:US:1123

[Jagermonster]

An easy way to tell the difference between the 40W and 60W amps is the height of the transformers. The power and output transformers in the 40W amps are roughly 3 1/2 to 4 inches high and in the 60W amps they are 4 3/8 to 4 3/4 inches high.

Another way is to measure resistances at the 9 pin phase inverter tube socket. In the 40W (7199), pin 8 will measure 47K ohms to ground. In the 60W (6AN8), pin 3 will measure 47K ohms to ground.

Well, finally got home after the holiday and checked the transformer size on my amp. Both measure about 4.5" tall from the bottom of the chassis. I'm pretty sure now this is a stock amp. Don't know why I got so obsessive over it, I think I'm just going to send it to a tech for an inspection anyway. Thanks again for all your help, guys.

[Jagermonster]

Finally got a definitive answer as to the Solarus tube question, provided by our pals over at Eurotubes:

"Conrad switched to the 6550’s in 1969 when the Genalex KT88’s because all but impossible to get, but there were no mods made to any of the amps. The switch to the diode rectifiers came in between 1969 and 1970 but only for the Sorado and the 100S and 200S amps."

I'm sure some of you guys were aware of this, but as a new Sunn owner, it's an interesting bit of trivia for me.