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Messages - DrewV

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Amplifier Discussion / Re: Fender Stage Lead 2 grounding out
« on: January 05, 2014, 08:22:42 PM »
here's the dope on the amp

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Amplifier Discussion / Re: Fender Stage Lead 2 grounding out
« on: January 05, 2014, 08:19:47 PM »
I'm at a dead end with this amp. I hate to throw in the towel, bbut as Kenny R says, " you got to know when to hold 'em, know when to fold 'em".  Thanks  guys for the excellent info, I just don't have the right tools for this baby. Hope your new year is "Bitchen"!! DrewV

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Amplifier Discussion / Re: Fender Stage Lead 2 grounding out
« on: December 17, 2013, 05:27:58 PM »
Ok Enzo here's what I've got.
 "Let's use plug numbers.  When you say you removed ALL multipin connectors, that sounds to me like it includes the transformer wires." That would be everything that can be unplugged from the board except P8

"SO just what is connected and not connected for your tests?"
I tested with everything connected. Then I tested with the output transistors disconnected. Then I tested with everything except the transformer disconnected.  At one point I tested the red leads from the transformer.



"APparently the output transistors are mounted off the board, on a heatsink, yes?"  Yes, with Q’s201/202/203 connected to the board  (via P5 and P6), I get Mohm readings on all legs of all three transistors. ( to the chassis) With the transistors disconnected from the board all reading are OL. Q201 (TIP29B) gives a 0ohm reading from the mounting base heatsink to the chassis but OL on all three pins to chassis ( collector not in contact w/ mounting base).
"Are the insulating mica or silicone wafers under the transistors?" Yes. 
"So are the bodies of the transistors insulated from chassis?" Yes

 "Current is still finding a way to ground.   So what exactly does find a way to ground mean to you?"  I’m going from points on the circuit to the chassis.

"It is appealing to look for bad parts, but the circuit is parts connected together, and a broken or missing connection is just as deadly to an amp as a shorted transistor." I’ve inspected the board ,touching up suspicious looking solder joints. Can’t see or smell anything else ( besides R 78) burning. C45 was OL so I replaced it.
Raising the line to about 2 VAC the LBL begins to glow brightly.
Thanks Drew

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Amplifier Discussion / Re: Fender Stage Lead 2 grounding out
« on: December 14, 2013, 04:54:00 PM »
 Q8 tests good out of the circuit.  Where to  next?  dv

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Amplifier Discussion / Re: Fender Stage Lead 2 grounding out
« on: December 14, 2013, 03:26:41 PM »
Yeah, I thought as much. I'll melt some solder and get back. Thanks Roly

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Amplifier Discussion / Re: Fender Stage Lead 2 grounding out
« on: December 13, 2013, 08:07:43 PM »
OK, the stage and studio amps are basically the same. There are id numbers on the main board which match those on the schematic.
Note that if all multipins are disconnected from the main  circuit board, current is still finding a way to ground.
 I removed D's 15 16 17 18 from the circuit. All tested good on a dvm diode setting. I remove Q12 fron the circuit and it tested good on both the dvm and trans checker .
 The output transistors Q''s 201 202 203 are chassis mounted. Q201 is a TIP29B.  It checked out good on both my dvm diode setting and my trusty transistor checker. ( I bought it at Radio Shack in 1983 ) I get a reading of 5.1Mohms between the B -C, but only with the positive probe on the base. Reversing the probes gives me a reading of OL.
 Q202 & Q203 ( MJ15003 ) likewise tested good w/both meters. All three OT's connect to the board via multipin connectors, so removing from circuit was easy!.
  A few days ago when I still had noise coming out of the speaker I noticed that touching the base of Q8 with a meter probe could make the sound come and go with a pop like noise. It's an RCA 1C04 pnp. A few minutes ago I retested it in the circuit with both meters. The transistor checker says its good. The diode check with the dvm says about .500v both ways between the emitter and the base. Can the circuit be causing this reading? B-C reads like a good diode.

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Amplifier Discussion / Re: Fender Stage Lead 2 grounding out
« on: December 12, 2013, 09:22:02 PM »
Testing Q12 in circuit it reads good. D17 was the only one I lifted a leg on. Early on I checked both windings coming off the transformer and got a good reading of + 37 / -37v. Tomorrow I'll pull Q12 to test out of circuit as wel as the other three rec diodes. Thanks Enzo I'll get back to you with my results manyana. Drew

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Amplifier Discussion / Fender Stage Lead 2 grounding out
« on: December 12, 2013, 08:25:15 PM »
Hi All, So, I'm trying to bring this amp back to life. Initially it blew both fuses between the transformer and the rectifier diodes. After replacing the fuses and bringing the voltage up slowly (variac + lightbulb limiter) I was able to get some sound from a line in source. However, when I tried to increase the V the amp started sucking current like there was no tomorrow. All transistors read good on a transistor checker.After some checking I found that R78 was burning up.   I can't figure out what is causing R78 to burn. I replaced a number of carbon comp resistors, the worst out of spec was R78, which was going open at 200 ohms. Every single diode reads good. Lifting the cathode leg of D17 eliminates the short. The electrolytes all check out good. I put a 9vdc charge on the filter caps which came back at about 7.5vdc.
I was going to throw in the towel on this amp, but it just bugs me that I can't figure it out. All insights appreciated. thanks Drewv
Attached is all the info on this amp. A few of the values and/or part numbers are different than what I'm looking at, but nothing major.

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Schematics and Layouts / 1980's Fender Stage Lead / Studio Amps
« on: November 17, 2013, 05:56:43 PM »
Hi All, I am restoring a 1982 Fender Stage Lead II. I  found the schematic / parts list / layout for the amp I have at http://www.stratopastor.org.uk/strato/amps/twoseriessolidstatefenders/twoseriessolidstatefenders.html.
They have more Fender schematics listed. I have attached the pdf. Enjoy dv

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Amplifier Discussion / Re: Light Bulb Limiter
« on: April 19, 2012, 12:58:17 PM »
Tom, Yeah that's how I've always done it. You'll know right away by the brightness of the bulb if excessive current is flowing.

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Amplifier Discussion / Re: Light Bulb Limiter
« on: April 17, 2012, 10:57:08 PM »
I'll just make a couple comments here. Regarding the level of bulb brightness, I have found that  different amps draw more or less current while "idleing" causing the bulb glow a little brighter or dimmer. Second, to prevent a situation like JM described always use a variac to bring the voltage up gently. If the amp is drawing excessive current you'll see it before you raise the V to high.

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Amplifier Discussion / Re: Light Bulb Limiter
« on: November 19, 2011, 09:55:16 AM »
You could probably stock up on a 20 year supply of incadescents for not much $$

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Amplifier Discussion / Re: DISTORTED OUTPUT
« on: April 03, 2011, 02:41:19 PM »
 Installed new parts. Amp is working. Thanks again DrewV

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Amplifier Discussion / Re: Light Bulb Limiter
« on: March 27, 2011, 08:28:14 PM »
I built one a few years ago. Works like a charm. I wouldn't want to make smoke without it! dv :lmao:

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Amplifier Discussion / Re: DISTORTED OUTPUT
« on: March 27, 2011, 08:26:00 PM »
JM
I use  a dynamic transistor tester, so I I'm confident none of the other transistors are bad. the transistor upstream from Q7 is Q1 TIP 29, (I think that's what you mean), which did get very hot once or twice, but it's a stout looking thing with a huge heat sink on it. It likewise tests good. R 25 (125ohm/5W- collector Q11) is 10% out of spec as is R52 ( 2.0ohm/5W- just prior to spkr output) is 25% out of spec. The only other thing I see right now is C1 (2.2uf/25V NP). It builds to OL rather quickly.
So, including Q7, that's what I'm going to replace. I've got an order into Mouser. I should be done by Wed. I'll get back with the results. Thank you for your insight. Drew

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