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Q & A / Beta Lead Ticking
« Last post by porcupine on May 16, 2018, 09:24:55 am »
I picked up my first Beta Lead for pretty cheap off Craigslist ($180!) and have spent the past couple days cleaning it and learning its ins and outs. I cleaned all of the jacks and pots and took a look at the PCBs to see if there were any obviously damaged components. No obvious damage, though it looks like someone added an electrolytic capacitor to the solder side of the preamp board.

Everything seems to be working, except the amp produces a ticking sound when Drive A is set below noon. The ticking is slow when the drive is turned counterclockwise and starts going faster as the pot is turned up. The pot works -- it adjusts the drive as it should, but it also controls this ticking sound. The tone of the tick is effected by the EQ knobs.

I plan to replace the electrolytic caps just as a general precaution, but does this sound like an issue with the transistors or ICs, or should I wait and see if re-capping solves it?

Unrelated question: when I use the Both input, certain EQ and Level settings seem to interact and in some cases lower the overall volume. Is this normal? I wouldn't be surprised if it was some kind of phase issue or EQ curves cancelling each other out, but I'm just not sure...
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Q & A / Re: Sunn Sorado Coupling Caps
« Last post by Soundmasterg on April 30, 2018, 07:08:31 pm »
Neither of my Sorado transformers says "Dynaco," although the ones in the Sonic that I had in the late 60's did.  When did the Schumacher trannies come in?  What do you mean by "tighter"  -   does that mean less low bass?  I picked up a couple of .25uF 6PS caps on ebay and may try them.  My filter cap job brought me to 110/50/22/22 if I remember right, thanks to your recommendations.  Inrush voltage with a Weber Copper Cap was tested at: 601V; A: 545V; B: 469V; C: 354Volts.  With the 5ARU tube, it was 576, 545, 463, 353.  Thanks so much for your help.  I've learned so much from this forum.

By the way, will I need to re-bias after changing coupling caps?

There should be an EIA code stamped into the transformer end bells.

http://www.triodeel.com/eiacode.htm

http://users.eastlink.ca/~mitchlane/EIA_Codes.html

I forget right now what the code is for Dynaco but Schumacher is 606.

Tighter would mean that the bass note will hold together a bit better than with the larger cap and be less mushy sounding. It is a subtle thing, and really just try it and see. Change both caps at the same time, then go back to the 0.1uF ones. Your ears will lose the memory of the sound during the time it takes you to switch between each, but if you play around a bit then you should be able to hear the differences.

The changeover likely happened by 1969 but some late 1968 models could have the Schumacher transformers also. No need to rebias when changing coupling caps...just make sure your work is good and the soldering is done well. All the usual safety rules apply for working with high voltage devices so if you don't know what you are doing fully, then please have others more qualified to do the work. The 6PS Orange Drops are radial caps so they will mount differently than the axial caps that were in there. Be careful about bending the leads and use needle nose pliers to bend the leads after the bend that they already have in them...do not bend right at the body of the cap, or you risk damaging the cap.

With the other changes you made to the amp, you have a stronger and tighter bass than it had stock, so the cap change will be slightly more of the same. Also, I will reiterate what I stated in those posts that you worked from for the cap job.....do not use the 5AR4 anymore in that amp unless you change the first cap to a size smaller than 60uF. The Weber Copper Cap or some other solid state rectifier must be used with the large first cap value or damage will occur to the rectifier tube, and possibly other things in the circuit. If you stick with the solid state rectifier/Weber Copper Cap then it will function fine.

Happy to help...keep learning and pass on what you have learned. Thats all I'm doing. :)

Greg
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Q & A / Re: Sunn Sorado Coupling Caps
« Last post by eddiemac on April 30, 2018, 05:42:32 pm »
Neither of my Sorado transformers says "Dynaco," although the ones in the Sonic that I had in the late 60's did (on second thought, it was probably the can cap that said Dynaco).  When did the Schumacher trannies come in?  What do you mean by "tighter"  -   does that mean less low bass?  I picked up a couple of .25uF 6PS caps on ebay and may try them.  My filter cap job brought me to 110/50/22/22 if I remember right, thanks to your recommendations.  Inrush voltage with a Weber Copper Cap was tested at: 601V; A: 545V; B: 469V; C: 354Volts.  With the 5ARU tube, it was 576, 545, 463, 353.  Thanks so much for your help.  I've learned so much from this forum.

By the way, will I need to re-bias after changing coupling caps?
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Q & A / Re: Sunn Sorado Coupling Caps
« Last post by Soundmasterg on April 30, 2018, 11:15:22 am »
The earlier ones often came with the 0.25uF Black Cats instead of 0.1uF, but either is fine. The bass response is a little tighter with the 0.1uF. The difference is because the early Sunns were a direct copy of the Dynaco mk.3 HiFi amp, which used the 0.25uF value. Later an engineer hired by Conrad tweaked the amps to be a little better for musical instrument use, and that is when the 0.1uF came in. The early amps also had Dynaco transformers instead of Schumacher, and slightly lower voltages. They seem to work better with the larger value cap than if you sub it into a later amp with the Schumacher transformers....likely because with higher voltages you get a wider frequency response and its a bit much with the higher voltages and higher value cap. Regardless, it is easy to swap the caps and see if you like it yourself or not. These days the 0.25uF value isn't as easy to find as a 0.22uF value. The 6PS series (polyester) of the CDE Orange Drops series comes in a 0.25uF value the last time I looked but I don't believe the M150's do, though I could be wrong. With the improved cap job (I'm assuming larger power supply caps?) the smaller coupling cap in that spot is likely a better choice, but YMMV.

Greg
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Q & A / Sunn Sorado Coupling Caps
« Last post by eddiemac on April 29, 2018, 08:27:00 am »
I have a May '68 Sunn Sorado with tag that shows KT88's.  Almost everything inside matches the Sorado (and 200S) schematic, except it has .1uF caps before the power tubes instead of the .25uF coupling caps the schematic shows.  I've seen pictures of other 200S, Sorado chassis with .1uF Black Cats in this same position (mine are obvious replacements  -  Mallory 150's).  Can anyone give me some insight on this situation, or offer a guess?  Am I better off with the .1uF?  I'm using JJ KT88's after a new, improved filter cap job.
     http://www.prowessamplifiers.com/schematics/sunn/Sorado.html
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Q & A / sunn mustang
« Last post by skuzzer on April 27, 2018, 05:28:24 am »
Hi I have an indian sunn which weighs about 3 ton. I have just got another sunn Mustang which is probably about 4 kilos. head is not the typical strat head. states Sunn Mustang. an authorised fender product. And on back of head the numbers  28-1100-906. has an allen key instead of bullet for truss rod. Any ideas where it is from and when ?? Tks Skuzzer
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Q & A / Re: 1971 Sunn Sonaro Amp Tubes..?
« Last post by BC Gearhead on April 16, 2018, 09:00:33 pm »
Hello fellow Sunn worshipers. I picked up this very amp yesterday, and thanks again for the great deal. Itís missing the bridge, filter caps,one input jack,fuse holder,power cord and the power transformer is definitely not original. Iím hoping the correct voltages are present when I have a chance to test. I probably wonít have time to look at it for a while but that amp has found a good home. I have owned a 2000s for 12 years as well as several small wattage vintage tube amps. I think the Sonaro is going to be perfect for the smaller rooms where I occasionally gig. As well as a 1974 Pre Bass I own a 4003 Ric so it might be fun to use both amps for the ric-o-sound output but I probably have to get in shape first to lift all a that gear :-D. Iíll post about the progress as it happens, might be a few months before I get to it and since itís in very good shape cosmetically for a 47 year old amp Iím going to take my time and do a nice job with the repairs.
Cheers
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Q & A / Re: 1971 Sunn Sonaro Amp Tubes..?
« Last post by EdBass on April 15, 2018, 11:20:01 am »
No problem, nice old amp if you can get it squared away. This is a gut shot of a 6/4/71 inspection date 200S, pretty much all of the stuff that isn't in your amp's chassis will need to be there for it to work.

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Q & A / Re: 1971 Sunn Sonaro Amp Tubes..?
« Last post by staceyz on April 15, 2018, 07:59:32 am »
Thanks for the reply & advice..!
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Q & A / Re: 1971 Sunn Sonaro Amp Tubes..?
« Last post by EdBass on April 14, 2018, 09:55:49 pm »
That '71 should be a 60/80 watt amp, the '71s I've had were 60 watters with tube rectifiers but I don't see the hole for the rectifier tube socket on yours.

12AX7
6AN8
6550 or KT88 X 2

There are a bunch of things I don't see in your pics. You need much more than just tubes in that amp, it's pretty hacked up. Looks like that old girl may have been pillaged for parts. That power transformer is gigantic, and while generally bigger is better in the world of transformer, it ain't right for your amp.

I suspect you could buy another functioning 60 watt Sunn for about the same or maybe even less money than it would take to rebuild that one to OE spec. My suggestion would be to take it to a qualified tech along with a schematic for a 6550/KT88 Sunn amp and get a estimate to revive it.
I can post or send you a schematic, but they are available all over the web.
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