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91
Q & A / Re: 1970 1200s restoration
« Last post by Tdlunsfo on April 20, 2017, 06:20:54 am »
Forgot to mention that the death cap has been removed and the polarity switch bypassed. I did pull some tubes a minute ago and the PI tube had an effect, the others had no affect. PI tube tests good. Also tried grounding rivets here and there with no effect. I did remove and leave out the big 20uf orange Mallory caps. These appeared to be added but I cant verify it. The are not on my version of the schematic...but then again the cap doesn't match the schematic 100% either.
92
Q & A / 1970 1200s restoration
« Last post by Tdlunsfo on April 20, 2017, 05:24:46 am »
I recently acquired a 1970 1200s for a song and trying to restore it. Here is where I am at currently.

Fuse holder replaced
Power cord replaced and grounded to chassis
Power supply cap can replaced.
50uf caps replaced
1000uf cap replaced.
2w resistors replaced on cap can
1w resistors replaced in bias circuit
Removed diode recitifier and wired up second 5AR4 socket. (This is the model with two sockets but sold with the diode)

Fired up the amp and it sounds nice and loud. The problems start with the hum and a weak tremolo. I checked the riveted grounds as they are known to be loose but they are tight. Will try some solder on them later today. My tremolo has the Sigma Datacell LDR module. I can hear it oscillate but its weak. I noticed mine is the -12 model LDR, but the schematic denotes 6 volts across the light. Should mine be the -6 model that I see being sold as NOS? All the old caps in the trem test ok as well as the transistors.

So I still need to check bias and reverb but wanted to get your opinions on the hum and tremolo first. Also, would like to know which LDR you guys have in your 1200s amps as information on this is limited.

Cheers!
DL
93
Q & A / Re: Line in to 200S power amp
« Last post by _peter on April 20, 2017, 04:37:45 am »
Hi,

of course, going to pin 2 of the 6AN8 (i.e. the grid of the triode section) is NOT the way to go.

For one thing, your mixer's output doesn't deliver enough voltage to drive the power amp. The triode phase inverter only has a gain of ~1. So you need another gain stage.

But above all, you will mess with the phase inverter's bias point when connecting something to its direct coupled grid - and possibly even destroy your mixer due to the high DC voltage.

Just go from the input jack to the grid of the 6AN8's pentode section, which is pin 8, if I'm correct. Shielded cable and a grid stopper wouldn't do no harm.

Cheers,
Peter


94
Q & A / Re: Unwired Rectifier Tube Socket Stock From Factory??
« Last post by Derrick on April 19, 2017, 06:00:22 pm »
Uhhh... I just got a notification that this topic was replied to but the replies were in mid November?!?!  OK, strange.  Well anyhow, what was the original wiring configuration... both 5AR4s wired in parallel?  I'd rather use two 5AR4s than a single solid state module.  Maybe I will get a notification to the next reply 6 months from now.
95
Q & A / Re: Line in to 200S power amp
« Last post by Cartoonist1 on April 19, 2017, 03:48:28 pm »
Thanks Isaac

I'll check this out. 
96
Q & A / Re: Cone Excursion
« Last post by eddiemac on April 14, 2017, 08:09:12 am »
I don't actually have a D140F anymore.  I didn't make that clear.  I was speaking about back in the day, and I know what you mean about getting "soft."  Mine did that  -  I even sent it back to JBL under warranty.  Naturally, they sent it back unchanged, but I did get a very nice letter asking me what I was talking about.
I appreciate your insights and wealth of experience, Ed.  I play blues in small clubs, quite often without PA support.  Your rig sounds really cool.  I just need one or two setups that can be stand-alone units, like we all used to play through (I'm 66).  The Fearfuls are useful for very large venues and outdoor events, and my Fearful 12/6 with 12 Sub gets rave reviews from audience and other musicians.  I think it sounds pretty darn good.  But the Sorado is apparently not the amp for it.
I have a K140, but it's been reconed.  So far, the Sorado has worked best with an EV 15B in an EV design box, but I plan to experiment with other cabs on the JBL.
97
Q & A / Re: Cone Excursion
« Last post by EdBass on April 14, 2017, 05:14:45 am »
Your D140 is probably at least 40 yrs old, it may be that it's just tired. The suspensions on a driver wear down and loosen. Reconing is a fact of life in the speaker world, just routine maintenance. Until recently I worked for a touring production company that ran stadium sized L-acoustic K series rigs, when they came off the road there were stacked pallets of drivers that needed to be reconed. Some had blown in use, but the majority of them were worn by hours in service and were getting "soft" so were reconed as preventative maintenance.

Modern drivers will take a bunch of power, but generally sacrifice tone and sensitivity. In the SR world accuracy and SPL are the keys to success, and nowadays watts are dirt cheap; so heavy surrounds, spiders, double voice coils/spiders, etc., are commonplace. You can beat the snot out of them and they will take it, but they need huge power to get to to acceptable SPL's.
In the era of the D140, a 100 watt amp was considered a MONSTER. Drivers needed to get all the SPL they could from the low powered amps of the day; diametrically opposed to "You can beat the snot out of them and they will take it, but they need huge power to get to to acceptable SPL's".

But we are talking about something else also. The D, K and E series JBL's were excellent Musical Instrument speakers. Originally the D's were AP drivers, and once they became popular for MI amplification (around the time of the "F" designation on the model), the "lettered" JBL's became MI drivers, and the SR drivers adopted a numbered identification system. MI drivers sound good when used in that application; the idea that the rig as well as the instrument make up the "instrument". Guitar players "get it", but some bass player don't. Which is fine, whatever floats one boat, it's music not rocket science.
I prefer my bass rig to be "musical", and like the majority of guitar players and many pro bass players my rig is an integral part of my tone. I currently gig with a '68 Sunn 200s into a Sonic I-40 cab loaded with a K140. I put it on a X stand at head level with a Heil PR40 stuck in front of it, and use a JBL PRX812W as a floor monitor in front of me. Much easier to transport than my big rigs, sounds absolutely phenomenal, plenty of stage volume. Let the PA do the "heavy lifting".  :wink:

Fearful cabs are far closer to a small SR cab than a MI cab, Eminence makes a real nice driver, lotta bang for the buck, but is amateur/semi pro grade as far as SR drivers go. The old "get what you pay for" scenario. a 3015LF is <$200, a 2226 is >$500.

The Fearful is an amateur, free ware designed two way SR cab. no reason it wouldn't sound nice, basic WinISD on a driver that Eminence provides amateur design assistance with, crossed over "by the book" with a 6" mid driver. Through another forum it developed a following of unenlightened "internet experts" for a minute, but was never taken seriously in the pro world.
Honestly, if you were looking for a pure unaltered bass guitar to ear sound, just run direct and use a professional monitor, there are myriad pro designed options available. There are powered 15" 2 way speakers/monitors starting at a few hundred bucks that you can plug straight into, that will absolutely destroy the GK/Fearful if you are looking for full range accuracy and need a free standing rig for your purposes. Heck, you can get a 1500 watt PRX815W for $900 that you can plug straight in to, even control it with an ios or windows device via bluetooth that will carry a FOH many times what that GK/Fearful rig is capable of. 

The bottom line is to play what sounds good to you. The only way you are going to even get close to the SPL of your GK rig with the Sorado is to put a bunch of efficient drivers with it, maybe 2 X 215 cabs, or mic it and run through the PA. But never in a million years will that transistor amp through a homemade PA speaker cop the tone of the Sorado rig; provided of course that your D140 is healthy.
98
Q & A / Re: Cone Excursion
« Last post by eddiemac on April 13, 2017, 11:27:12 pm »
I'm using a 1-15 cab as I did with my Sonic (back when sound levels were more humane).  I think if I was using 2-15's, things would be better.  I know the JBL D140 has about 1/4" Xmax, if that.  It always looked like it was moving more than a half inch on the deep notes, and now my 15 sometimes bottoms out on the low notes when hit hard.  A Fender Showman has better damping abilty.  I played a gig tonight and started out with the Sorado into a Fearful 15/6, which has an Eminence 3015LF with massive excursion ability.  After two songs, I switched back to my Gallien Krueger.  It just sounded better.  But then, 350 watts compared to 60 tube watts is not a fair comparison.  I will plan on using the Sorado on quieter gigs in smaller rooms, which is why I got it in the first place.  By the way, Soundmasterg, I am in your debt.  Your postings about cap replacement, in our modern age, has been my guide to reconditioning my amp.  Thanks!
99
Q & A / Re: Cone Excursion
« Last post by bigobassman on April 13, 2017, 06:27:27 pm »
I've had speaker guys tell me that movement is actually a positive.  I don't know one way or the other, but I've had lots of speakers exhibit that movement with great sound and longevity.
100
Q & A / Re: Cone Excursion
« Last post by Soundmasterg on April 13, 2017, 04:25:50 pm »
I would guess that it probably would do that with any tube amp. Tube amps don't have as high of a damping factor (ability to control the load) as solid state amps so the speaker isn't controlled as well. Maybe with the Sunns it might be because they are UL (ultralinear) as opposed to most other tube amps, but I am not sure about that one. All of the Sunn amps were based on Dyncao hi-fi amps, which had full range frequency response, and in the case of a Sunn 2000S, they will amplify cleanly down to 10Hz at least with the Dynaco transformer models. Your speaker cabinet can't reproduce frequencies that low, but it may just be that the Sunns have more energy down low and make the cone move a lot.

What is the problem though? The original amps and cabinets worked fine together even with the excessive excursion and I would bet modern cabinets would also work fine. Just play it and enjoy the sound and feel.

Greg
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