New Member- New (old)amp Sonola 98-RT

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New Member- New (old)amp Sonola 98-RT

Postby kcaccavaro on Thu Jul 13, 2017 6:33 pm

Hello everyone, I've been lurking around for a few months and I submitted a post a few weeks back that hasn't been OK'd by the administrator yet. I recently picked up a Sonola 98-RT and I'd love some input on the best way to care for this old amp. It's in amazing condition and I'd like to keep it that way.
Hopefully this post will be approved,I'd love to share pictures of the amp since there isn't a lot of info out there.
Thanks
Kevin Caccavaro
Lexington, SC
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Re: New Member- New (old)amp Sonola 98-RT

Postby Dean Jr. on Sat Jul 15, 2017 5:48 pm

Pics? History of this amp...maker? Guild??? IF so,
At any rate, it is of an age that dictates that the electrolytics need attention, ime....as does the power cord. Tech time, imho. I don't play old amps until they are made fresh and safe.

Like this?
http://www.marcsilbermusic.com/inventor ... nstid=2275
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Re: New Member- New (old)amp Sonola 98-RT

Postby kcaccavaro on Tue Jul 18, 2017 4:06 pm

A little history on the amp. My brother was given the amp by his neighbor when she heard he was into vintage electronics. Apparently her husband got the amp as a kid when his parents made him learn the accordion. He lost interest pretty quickly and the amp was stuck in a closet where it's sat under the dust cover ever since. My brother doesn't play guitar, but he knows enough to recognize a cool old amp so he called me up and we worked out a deal- now she's mine.
It's got a Guild label and S/N and a couple of the tubes are Guild labeled RCAs. It also has the original wooden foot switch for reverb and tremolo and the original amp cover, too. Jensen speaker, RCA and Tung Sol tubes, and I noticed Vitamin Q caps in there, too.
A little history on me, I've always been interested in tube amp repair, but never really had much experience with it. So I've been taking the cautious approach and trying to learn as much as I could before opening up any amp. I'm comfortable with working safely and understand about discharging capacitors,etc. So I'd like to go through the amp and make sure it's working as it should. I'd welcome any advice, direction, corrections from you good folks on the board and I'm not afraid to go to an amp tech if I get too over my head.
The first thing I did was replace the power cord with a 3 prong grounded cord and then I powered it up using a Variac to ramp up the voltage slowly. I got it up to about 85 volts and it sounded great, but then I heard a pop and smelled smoke, so I cut it off to investigate. Looks like filter capacitor can popped since I see a bunch of brown goop coming from the top of the can. I looked over the other capacitors and didn't see any obvious signs of damage. No bulging or leaking. Will a multi-meter help me at all to determine if the caps are still in good condition? I ordered a new 40/40/40 525v CE Mfg. cap which just showed up, so next thing i need to do is swap it out.
I've added a few pictures below.
Thanks,Kevin
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Re: New Member- New (old)amp Sonola 98-RT

Postby Dean Jr. on Tue Jul 18, 2017 4:19 pm

The bias cap, which is an electrolytic, needs to be replaced, too. I am curious.....how did you go about the Variac application? How much voltage to start with and how did you increase the voltage over what period of time?
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Re: New Member- New (old)amp Sonola 98-RT

Postby kcaccavaro on Tue Jul 18, 2017 6:31 pm

I started with 25v and increased by 10 volts every 30 minutes. As I mentioned, I stopped at 85 volts once I let the smoke out. Too much too fast?

I'm not sure which is the bias cap,but am I correct in assuming that the red .05mf 600v cap between the switch and fuse is the "death cap" and should have been removed when converting to a 3 prong cord?

A couple more pics:
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Re: New Member- New (old)amp Sonola 98-RT

Postby Dean Jr. on Tue Jul 18, 2017 7:04 pm

see that 50mfd/25VDc e-cap in the lower right of the first picture in your last post? I am going to think that that is probably your bias circuit cap. You can easily trace the circuit to confirm this. On the schematic, the bias resistor is a 250ohm resistor that is tied to between the 6v6"s pin 8 cathode and ground. There is a 50mfd/25VDC cap in parallel with that resistor.
Nice, clean amp.....jealous, I am. :mrgreen:
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Re: New Member- New (old)amp Sonola 98-RT

Postby kcaccavaro on Tue Jul 18, 2017 7:06 pm

A pic of the back after converting to a 3 prong grounded cord:
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and the leaking cap soon to be replaced

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Re: New Member- New (old)amp Sonola 98-RT

Postby Dean Jr. on Tue Jul 18, 2017 9:05 pm

The date code on that multisection cap can is the 32nd week of 1963....fyi. I personally would not play that map much until it is fully serviced.
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Re: New Member- New (old)amp Sonola 98-RT

Postby jaywalker on Thu Jul 20, 2017 4:03 am

Dean Jr. wrote:see that 50mfd/25VDc e-cap in the lower right of the first picture in your last post? I am going to think that that is probably your bias circuit cap. You can easily trace the circuit to confirm this. On the schematic, the bias resistor is a 250ohm resistor that is tied to between the 6v6"s pin 8 cathode and ground. There is a 50mfd/25VDC cap in parallel with that resistor.
Nice, clean amp.....jealous, I am. :mrgreen:

The schematic as I see it reads "20" in the rc bias so verify that they are in parallel...I can't tell from the pic. If they are then go with what's in there for a replacement value.
https://www.fliptops.net/ has the dual 20uF/450v if that's what the yellow firecracker cap is and probably have the sectional 40/40/40uF/450v can cap too. Be sure to compare base diameters new and old.
Straighten out the power section first then you probably need to replace all the other electrolytic capacitors too.

I'm green along with Dean Jr. This is going to sound good!
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Re: New Member- New (old)amp Sonola 98-RT

Postby jaywalker on Thu Jul 20, 2017 4:15 am

I'm curious as to which model speaker that is...look on the outer rim for P12R or some such, then some numbers starting with 220-
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Re: New Member- New (old)amp Sonola 98-RT

Postby Vortexion on Thu Jul 20, 2017 8:41 am

Hi Kevin. Lovely amp! :excited:

Given its age and the fact that it hasn't been played in donkey's years, we can take it as a given that ALL of the electrolytics will need replacing before any attempt is made to apply power, even with a variac. There's no point wasting time trying to establish which of the electrolytics are "still OK' - they're over 50 years old, so they'll be dried up and fit for the scrap heap. There ain't no such thing as a good NOS electrolytic. Powering them up now is like asking someone who's been asleep in bed for over 50 years to get up and run a marathon. Just replace the lot.

It's curious that that big cap has sections that are 40uF instead of the 20uFs on the schematic, but not surprising. Manufacturers often strayed from their published schems according to what components they had in stock/were short of, and back then the value tolerance of electrolytics was so wide of nominal that it was very much a case of "20uF? 40uF? Meh - who's counting..." :mrgreen: Same applies to that 50uF 25V cap if it is the one in the cathode bias for the output tubes: the factory was probably just short on 20uF caps that week.

Anyway, as Dean Jr has already said, don't do any more powering up until this baby has had a FULL overhaul.
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Re: New Member- New (old)amp Sonola 98-RT

Postby JJman on Thu Jul 20, 2017 11:02 pm

I think I see Astron coupling caps. They often leak DC when tested. It's a big hidden tone and signal robber and heats up pots. Proper testing means disconnecting one end in most cases. Post overhaul it should be a fantastic amp, being from the same year as I. :cheers:
-If it says "Vintage" on it, it isn't.
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Re: New Member- New (old)amp Sonola 98-RT

Postby Dean Jr. on Thu Jul 20, 2017 11:17 pm

Ime, the Astrons....the yellow molded ones...are more reliable than are the paper-in-oils that are located in other parts of the board. but....everything is suspect until proven to be good, right? I have replaced ALL of the PIO caps in addition to all electrolytics in a '52 Pro, and when finished it sounded terrible. I went back in checking resistor values.....all of the resistors on the board were way out of spec. Only the input resistors, which carry no current, were good. The amp sounded fantastic after the resistors were replaced. However, in a closet queen like this one, the resistors may never have been subjected to enough hours of current to have been compromised.
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Re: New Member- New (old)amp Sonola 98-RT

Postby kcaccavaro on Mon Jul 24, 2017 5:20 pm

Thank you all for the great info. Just to update, I listened to your advice and I have not been playing the amp until I get it sorted out. Also, as much as I like a good challenge, I recognize I don't have enough experience to service the amp properly. I'm ok with soldering and swapping out components, but I don't know enough to troubleshoot and I don't want to learn the hard way on this amp.
I was given the name of a good amp tech about an hour and a half away, so I'm going be patient and bring it to him for inspection and repair as needed.
I already ordered a replacement 40/40/40 525V cap for the one that popped and It's a drop in fit for the bad one. I'll ask the Tech install it and check out the rest to see what else needs to be replaced. Any ideas on the ballpark cost for a service and re-cap?
jaywalker asked about the speaker: It reads C12R C7423-2

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The short time i did play the amp it sounded great, so I'm excited to see how it turns out.
I appreciate all the input and I'll keep you all posted on the progress.
Thanks,
Kevin
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Re: New Member- New (old)amp Sonola 98-RT

Postby Dean Jr. on Mon Jul 24, 2017 8:36 pm

C12R...ceramic magnet. I figured that under that bell cover would be a flat ceramic..given the age of the amp. The date code will will farther up on the left side of that speaker.....220.xyy.....X being the last digit of the year and yy being the week of the year.
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