Recent Posts

Pages: 1 [2] 3 4 5 ... 10
Q & A / Re: Which bulb in tremolo circuit for 68 Sceptre?
« Last post by patlaw on February 27, 2018, 06:30:29 pm »
If someone would put one of the SM-1 modules on the bench and do a voltage-to-resistance plot, that module could be duplicated. That is, plot a curve where 1v = X1 ohms, 2v = X2 ohms, 3v = X3 ohms. While I have a working SM-1 module, I'm not brave enough to try to take it out of the circuit to measure it. Like Conrad said, it's nothing special, but you do need the right values of incandescent lamp and CdS photocell.
DIY / Re: Beta Bass 1x15 Combo Repair/Refurbish Project
« Last post by Ryan Phelps on February 27, 2018, 06:18:34 pm »
Nice! Keep us posted on your progress.
Q & A / Re: Sunn logo history
« Last post by patlaw on February 27, 2018, 06:18:06 pm »
I took a picture of mine. It's definitely the old stuff. The Acoustone 4540 compares very favorably except that the sample on the website is upside down from my actual cabinet.
Q & A / Re: Sunn logo history
« Last post by EdBass on February 27, 2018, 06:16:06 pm »
Probably the rectangular pattern. The and the rectangular pattern were post '68, however there were some anomalies between model years with several parts, probably to use up existing parts inventory.
Q & A / Re: Sunn logo history
« Last post by Ryan Phelps on February 27, 2018, 06:12:40 pm »
I would not rely upon the Sunn badge....too easy to change. The 1st style grille cloth is black and silver in a fine diagonal pattern, similar to Traynor. There are plenty of threads on this. The 2nd style grill cloth is somewhat similar to Fender mid-sixties cloth except turned 90 degrees so it runs vertical. Wendell Fabric still makes this 2nd style (or a very close version) but you have to buy a minimum of 5 yards....a bit over $200 as I recall.
Q & A / Re: Sunn logo history
« Last post by patlaw on February 27, 2018, 01:42:38 pm »
...they added the "" in '69; the same time they switched to the rectangular pattern grill cloth.
EdBass, I'm trying to find new grill cloth for my 1969 Sunn Sentura II. Is the presence of the "" on the logo plate an accurate indicator of whether the grill cloth is pre-69? I don't know when in 69 mine was made.
Q & A / Re: Beta Lead A channel barely works but B channel works great..
« Last post by evilroot on February 26, 2018, 11:34:51 pm »
loudthud's advice is a really solid start.  Given I'm working on a nearly identical unit right now I might be able to help a bit.

Like he said if it's more than contacts things get more complicated.  But I have more questions . . .

Are you comfortable with taking it apart physically?  Can you or do you know someone that can desolder and solder components?  Do you have access to and know how to use (or know someone who does) a quality digital multimeter?
Q & A / Re: Beta Lead A channel barely works but B channel works great..
« Last post by loudthud on February 26, 2018, 09:20:41 pm »
On the back of the amp there are three effects loops. One for each channel and one Master (effects both channels). you want the one for channel A. These jacks should be marked "To Accessory Channel A" and "From Accessory Channel A".  Connect a patch cord or a known working guitar cord from the "To" to the "From". If this restores the function on Channel A, a squirt of contact cleaner (such as DeOxit brand) into the "From" jack should fix the amp. If not, you need someone that can troubleshoot down to the component level with an oscilloscope to repair the amp.

Edit: Changed the jack that might need the squirt of contact cleaner to "From". That's the one with the contact that completes the signal path when no effect is used.
DIY / Re: Beta Bass 1x15 Combo Repair/Refurbish Project
« Last post by evilroot on February 26, 2018, 06:51:03 pm »
Didn't take nearly enough pictures, but I've been working on it the past few days.

First up, the speaker seems to be original and is in fantastic shape.  No sign of any dry rot whatsoever and I hooked it up to a separate amp and it sounds great!  Pots are all extremely smooth without any gritty feeling.

Downloaded the service manual . . . the one of Fender's site is a poor scan but the archived one linked on other threads is missing a lot of pages.  I'll take what I can get.

Pulled the actual amp head out and got the boards into "service position".  3-prong plug in perfect shape.  Everything is amazingly clean. I wonder if it was just hardly ever used or if someone else cleaned it previously . . . but nothing showed any signs of ever having been taken apart..

The culprit was almost immediately apparent after a few basic tests.  I noticed a pair of TO-220 power transistors in the corner of the power board with a lot of glue, and one tested bad (Q11, a TIP30).  I'm guessing due to the crappy clip-on heatsink, and I'm pretty sure its TIP29C partner should have had a heatsink too.

Also the large input filter caps tested very poorly.  Not outright failed but not good either.  So they'll get replaced.

Since there are only two values of electrolytic buffering caps (2.2uF 50V bipolar and 10uF 35v)  in the entire unit I figure I'll replace them all while I'm at it.

And that brings us up to today.  Here are the new parts from Mouser:

I installed them all earlier.  Tomorrow I'll hook it up and see what happens!
Q & A / Beta Lead A channel barely works but B channel works great..
« Last post by ChagaAlaska on February 26, 2018, 04:08:46 pm »
Hello! New to the forum and new to owning a Sunn.

Just received my Beta Lead and the A channel barely barely works. Drive, bass,treb, mid, level all work but its just so quite.. I can talk louder than level and main volume cranked for that channel.
B channel works great and is extremely loud. While using both channels I tried to adjust channel A drive and level and could not hear a difference.

The head is plugged into a Marshall 4x12 8ohm cab

The channel isnt dead so there must be something I can do.

I play in a Funeral Doom band here in Alaska and amp techs are non existing.

Thanks for you time! Any feedback would be greatly appreciated.
Pages: 1 [2] 3 4 5 ... 10