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21
Q & A / Re: Original Model T questions.
« Last post by Isaac on May 18, 2018, 11:38:43 am »
There is no difference in the amp. The Model T was intended to be an "everything to everyone" amp, used for guitar, bass, even keyboards. The only differences were in the speakers.

As for your amp and its mods, can you read a schematic diagram?

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Q & A / Original Model T questions.
« Last post by RacerX on May 18, 2018, 10:16:29 am »
Hello, this is my first post and I have looked around the internet and this forum and can not find the information I am looking for. I have an original Model T that I bought at an auction in 1990 and never really used it. I am guessing that it has been heavily modified, but I can not find any pictures of the circuitry of an unmodified original Model T to compare it to. Is there a place where there are some pictures posted of the insides of a Model T with or without modifications?  I also wondered if a modified amp lost value because of the modification?  Or were there some modifications by the factory or certain people that increased the value?  Sorry for the edit, but I now have another question. I was reading the sticky post about the Sunn catalog and for 1974 they list both a Model T bass and a lead amp.  What distinguishes the difference between the two?   Thank you in advance for any help.
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Q & A / Re: Beta Lead Ticking
« Last post by porcupine on May 17, 2018, 06:30:54 am »
Played through it some more, and I'm thinking something must be wrong with the Both input. I can get a good sound through Channel A or B and set the other channel exactly the same way, but when I plug into Both the sound is substantially different. For example, if Channel A bass is set to 5 and Channel B bass is set to 5, playing through both will give a much thinner sound than playing through just A or B. Turning the bass down (!) or up on one of the channels will increase the overall bass response, but the 4-7 sweep of the pot will sound really thinned out. The mids don't behave like this, and I'll have to test some more to see if the treble is doing that. I think the pots are fine, as they work as they should through each channel individually.
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Classified / WTB Sunn Beta Lead
« Last post by ZackS on May 16, 2018, 08:11:32 pm »
As the title states I'm looking to buy a Sunn Beta Lead. Saw one on my local craigslist recently and got so excited about the prospect but it was sold before I pulled the trigger.

Looking in the $225 range.

I'm in Rochester NY 14623 and would be willing to drive within a 2ish hour radius of that, farther shipping is always an option.

Willing to put more $$ into it if it has the pedal.
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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?
28
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
30
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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