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6550 tube in an ARC Ref 5 SE

Hi folks, I’m trying to learn some about amplifier design and function here.

My story: I have an ARC Ref 5 SE. I stopped getting sound from it in August. Wasn’t sure what was wrong, so sent it to ARC for repair. Took a while, apparently due to their factory moving or something. Got it back last weekend, reported as “general repair” on the invoice; inside looked like they had cleaned it. Reinstalled the tubes and ... still no sound. Looking at the unit while on, I noticed no glow from the 6550 tube. It had about 1500 hours on it, so could have reasonably been at the end of its life. I therefore bought a Tung sol 6550 from the tube store and installed it. Now I see glow again, and the sound is back.

Ok, so I’m not gonna grouse about ARC not apparently testing the tube, rather, my interest is piqued, and I would like to learn here. The 6550 and its accompanying 6H30 are listed as part of the “voltage regulator” circuit as part of the power supply. My question is this: what exactly does this circuit do in a preamp, and why does the sound stop when the 6550 fails? Please explain in English, as I have no background in electronics. Just trying to learn here, and thanks in advance for teaching the newbie... the internet was pretty unhelpful on this question

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5 responses Add your response
tomic601's avatar
tomic601
12,914 posts
 
try searching

6550 tube as regulator in power supply ARC

topic covered for ARC power amps in some detail in Audio Asylum DIY sections....but the basic concept will apply for phase splitters, screens, etc in the preamp

also Brinkman use a 6550 in the turntable power supply...

Andy at Vintage Tube could also take you thru it as well as recommend a great NOs replacement...I run a USa made Tung Sol in my REf 5se.......
lalitk's avatar
lalitk
5,544 posts
 
Hope this article helps!

https://www.audioxpress.com/assets/upload/files/bicknell2890.pdf
smoffatt
205 posts
 
Hi. Had the same issue with my Ref3 LE a couple months ago. I was listening to some music one night and suddenly nothing. I looked at my Classic 120´s and all the tubes were lit. I looked in the Ref3 and my vintage Tungsol 6550 black plate is dead. Removed it put it on my Hickok tube tester and it tested strong as brand new????
I replaced it with a brand new SED 6550 I had kept as a spare. The tube would not light up at first but did a few minutes later. It stayed lit for a few hours and then went dead the same as the Tungsol. 

I sent an email to ARC detailing the issue. They were very helpful!! They asked me to send the unit to them as there is a major problem in the power supply.

Reading your post I am glad I did not. Anyway, the problem was the solder joint on the tube socket pins were cracked which cause the tube to go on and off intermittently.

I took the unit to a tech I know and he’s redone all the cold solder joints he could find (including the problem socket) and all is well now.

Having sent the unit back to ARC from Canada would have cost minimum $150.00 each way plus a new tube which I didn’t need and they would have missed the cracked solder joints on the tube socket. I got the work done for $80.00.  

noromance's avatar
noromance
9,821 posts
 
ARC et al, repeat after me; tube sockets were never meant to be on a printed circuit board. 
motorcyclphil's avatar
motorcyclphil
19 posts
 

I have had no issues with ARC probably 20 years now except for the HD220 Hybrid amp which stopped working and it turned out to be a universal problem, ARC fixed it for free even though the warranty had just ran out but would not fix it again, got rid of it and got their DS450 mono amps and with some fuse upgrades and power cord upgrades sounds better then the HD and runs cool vs HD super hot temp. All and all very happy with ARC gear and I will be sticking with that brand.

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