Resistor smoking: Wollensack repair

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Old 07-29-18, 03:29 PM
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Resistor smoking: Wollensack repair

I have a 1963 Wollensak that mechanical functions but plays no sound. I opened it up last week and noticed a completely fried resistor. I ordered a replacement, started up the reel deck and immediately starting smoking from the same resistor. I am not too inclined in electricity, I have been teaching myself how to read the schematic, but I believe the solution may be out of my comprehension at the moment to diagnose why it is doing this. I am asking for any help at all, or a direction to look at to stop this resistor from going up in smoke.

Here is snapshot of the schematic. The resistor that is smoking is labeled. I can provide all labeling information to what each number/letter that it corresponds to.

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Last edited by PJmax; 07-29-18 at 09:24 PM. Reason: added cropped pic of schematic
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Old 07-29-18, 04:47 PM
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Welcome to the forums.

Knowing those machines..... the two power supply capacitors are dried out.
I just replace them automatically. You could test them.
It is possible that something hanging on the 300v supply is also shorted/leaky..... but doubtful.

Replace C1 - 60-60-50uf @400v
Replace C2 - 25-20-20uf @300v
I'm just guessing at the voltage ratings. It will be on the caps. Both caps are three section cans.
 
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Old 07-29-18, 07:52 PM
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You are a godsend my friend!! I have posted in a lot of places with little to no answers, and you have given me hope! I THANK YOU!!

You are very close to the ratings, C1 is 60/50/50uf @350v and C2 is 25/20/20 @300v... although I am having a very hard time finding anything to match those ratings online. Some come close, I found a 350v 40/40/40 but that is the closest I have seen. Not sure if my google fu is lacking from my wording, not quite sure. Any suggestions where to look for these?
 
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Old 07-29-18, 08:14 PM
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I will check around for you. It is ok to go slightly over the uf ratings as it's used to filter the DC supplies.
The AC ratings must be the same or higher.

Look at places like Allied electronics or Mouser electronics.
 
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Old 07-29-18, 08:25 PM
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These caps are going to be expensive. It appears they are no longer in mainstream production. In a case like this I would use my oscilloscope to find out which sections were bad and possibly replace just the bad sections.

https://www.tubesandmore.com/product...50v-40404040uf
Google/search=3+section+electrolytic+capacitors

I would look at the schematic and see what is attached to the 300v supply. That would eliminate a possible problem on that line causing the resistor to burn. Is there an online link to the full schematic ?
 
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Old 07-29-18, 09:01 PM
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Dang, figures lol. That is the exact one I found as well, it has the right voltage for C1 but under uf rating, and above C2 and over uf. I tried looking at the schematic myself to see where it leads, it looks like it leads into the bias oscillator, which would make sense because there is no sound, but here is the link

I do not have a oscilloscope, so if that is what needs to be done there are a few repair shops I can take it to and they should be able to get the job done. That is my last hope though, would love to do it myself, but it is what it is if that's what it comes down to
 
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Old 07-29-18, 09:05 PM
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There is also this one that is a bit closer to specs, just a hair off
https://www.tubesandmore.com/product...50v-50505050uf
EDIT: Never mind that is a quad
 
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Old 07-29-18, 09:18 PM
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A quad is ok. Just use three sections.

If the bias osc is the only 300v connection..... try to disconnect the 300v supply to lead 1 of L1. That will eliminate the 300v supply as a problem. I can see L1 on the print but not how it's connected.

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Do you have a variac ? Turning the AC up slowly while measuring at the resistor will save you from having to keep replacing it.

-----------------------------------------------------------------------------------------------------------------
I went back and relabeled the diagram in post 1. The problem cannot be past the red X because that 47K ohm resistor is too high to cause a load. The problem is one of three things..... a load/short on the 300v line, possibly a fault on the 280v line or C1B or C1C is shorted.
 
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Old 07-29-18, 09:42 PM
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I will disconnect it tomorrow, give it a shot, and update. Just to be clear, you mean disconnect it and turn it on to see if that resistor continues to burn right? Just want to be 100% sure. If it continues to burn than the problem is the 280v connection, if burns it is isolated to the 300v connection?

I do not own a variac either, this is my first project with any electronics, so I am kind of learning as I go at this point.

Would that quad be alright even though it is off -10uf on one section?

The only reason I can see that L1 is connected to the 300v is there are only 2 300v indicated on the schematic. One with an arrow and the other with a connection dot, so I can only assume that these are continuous of each other. Maybe separated to conserve space and fluidity on the schematic.
 
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Old 07-30-18, 06:44 AM
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You will have a few options:

the cleanest, but most expensive is to have a new can capacitor designed and built: https://hayseedhamfest.com/pages/request-quote

option two: is to abandon and disconnect the original caps and use discretes, below the chassis, if there is room.

option three: open up the can(s) with a cut off wheel near the base, and pull out the messy guts. Install new leaded caps inside. replace the can, gluing the joint with JB weld. This is a fair amount of work, depending on the accessibility of the twist tabs and the components soldered to the tabs.

I've done option 2 and 3 on various classic tube gear with good results.
PJ has good links, add digikey also.

two cents of advice: smoking resistors are not caused by defective resistors; almost always true.
 
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Old 07-30-18, 09:12 AM
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Is this what you mean by option 3, rebuilding the can? If so I think this may be the option I go with, but I am having a hard time finding replacement capacitors with matching specs, and if I do they are quite expensive in themselves, about $20 each. There aren't too many wires on the twist tabs, just 2 wires each that are pretty accessible.
Correct me if I'm wrong but I need 2x 50uf @350V and a 60uf @350V? At that price point it might just be worth seeing how much a custom built one may cost. I'd be looking at around 60$ just for the parts and then the work, so a little extra on top to have one built may be the better option, but like I said I am not too sure that is exactly what I am going to need.

If you could, how would descretes work? Having little knowledge I am kind of following the schematics to a T as much as I can, so going out of that realm is a little daunting for me, but am willing to learn and look into it as a viable option.

EDIT: Also still wondering about this one that is rated 10uf under one of the ratings on the original can but matches the other ratings https://www.tubesandmore.com/product...50v-50505050uf
 

Last edited by chuck_goodman; 07-30-18 at 09:28 AM.
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Old 07-30-18, 11:01 AM
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https://www.digikey.com/product-deta...668-ND/1245997

I'm getting about $2.50 for each.
 
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Old 07-30-18, 11:38 AM
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Ahh ok, I was going with exact specs, didnt realize I could go over a bit for each. 3 of these will do the trick?
 
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Old 07-30-18, 12:28 PM
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Originally Posted by chuck_goodman View Post
Ahh ok, I was going with exact specs, didnt realize I could go over a bit for each. 3 of these will do the trick?
These capacitors are used as filter capacitors in this application. The more capacitance the better (more filtering). In other applications such as motor capacitors, the capacitance value is important, but not here.
 
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Old 07-30-18, 02:22 PM
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if you do restuff the can, make sure the diameters of the caps all work out to fit. Either geometry or a 2D drafting tool.

The other trick with re-stuffing is the unsolderability of the aluminum can. You need to bring out the NEG combined lead to something solderable. I think the twist tabs are solderable. You will reuse the phenolic insulator with the geometric stamps on it.
 
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Old 07-30-18, 03:56 PM
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Will do! Thank you all for the help, I can't express how much it is appreciated. I will post back here once I have everything in hand and take my best shot at rebuilding
 
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Old 08-09-18, 02:54 PM
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UPDATE: IT WORKS!!! I ended up getting the part custom made, it was about 35$ so I figure that was cheap enough to have it made and done professionally. Got the piece in today, soldered everything back, and it works like a charm! Thank you to everyone here, You all are truly amazing, and I can't thank you enough!!!
 
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Old 08-09-18, 04:10 PM
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Good job ! Thanks for the update.
 
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Old 08-11-18, 10:57 AM
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Follow up question for y'all, I have a pretty serious 60hz hum coming out of the speakers. Did a little research on it, and it seems like it is most likely the other electrolytic capacitor. Safe to say just replace that one as well? Everything sounds great, just have a pretty loud hum from both speakers, louder in the right side however
 
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Old 08-11-18, 11:05 AM
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It could be that other electrolytic cap since it's common to both channels.
Without using test equipment like a scope... it's going to be trial and error.
 
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Old 08-11-18, 12:47 PM
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If the unit has gone unpowered for more than 6 months during its 55 year life, I'd say all your electrolytics are suspect.

I've got to re-cap my guitar amp that's even older than your Wollensak. If I can hear the 60 cycle, it must drive others nuts.
 
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Old 08-11-18, 04:53 PM
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Ahh thanks for the advice fellas. Going to get a new can and give a swap. I would suspect it went many years with no play haha
 
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Old 08-17-18, 04:13 PM
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C1 and C2 are designed to kill 120Hz hum. If you really have 60Hz hum, that might be a tube issue with the filament, or maybe it is indeed a 120 Hz hum issue. My ears can't tell the diff, unless I listen to a test signal first!

OR, 60Hz hum from an input with bad ground, etc.
 
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Old 08-20-18, 10:50 AM
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I am not 100% certain if it is 60hz or 120hz. I have been listening to the differences on a few sound clips. I was listening the other day when I started to think that it was a 120hz because it was a little bit more of a buzzy hum, when a 60hz sounds more like a straight up hum. I get the can today, so in a few hours I will know for sure if that can was the issue or not. I am really hoping it isn't a grounding issue though. That is something I am not willing to mess around with haha
 
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Old 08-20-18, 11:07 PM
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UPDATE: So I got the new can in, it appears that it did help much, but the hums seem to be coming from more than one location. The left side appears to have a strong, decently loud, hum. Sort of buzzy, and is constant from the time the reel deck is turned on. The right side still has a hum that is lower in sound and appears to grow after being turned on for a few minutes (appears after about 30 seconds). Is it time to turn to test the tubes? If so, any advice to start testing them individually? There are 7 tubes total, 2 7591's and 4 6EU7's and 1 6C4. I was possibly thinking about taking one out at a time and see if this changes anything in the output. Is this a safe way to test them out?
 
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Old 08-21-18, 06:22 AM
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there is no oscilloscope in arms reach?

You could pull the preamp tubes L and R to see if the hum starts before or after that point. Work towards the output stage.
When you say "as soon as the deck is on"; does that mean before even the tubes warm up? If so, then that tends to point to the very last stage.

I should ask first: is all this hum coming from a speaker/amp? or, non-electronic?
 
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Old 08-21-18, 06:24 AM
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Can you relate the schematic to the parts in the chassis? Do you understand tube audio amplifiers?

You can go through the amplifier stages, shorting the control grid to ground. This will kill the audio. If the hum is still there then the hum was generated in that stage or a succeeding stage. If the hum disappeared with the audio then the hum was generated earlier. (If you don't understand this paragraph then you should not perform this test yourself since a wrong move with an alligator clip or test probe can cause damage.)
 
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Old 08-21-18, 10:27 AM
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No oscilloscope around unfortunately. This is my first time fixing anything electronic, and I just moved to a new state so I have no one that I know that may have one, so electronic diagnostic tools are unavailable to me.

I will clarify a little bit more of what I meant, posted that comment really early this morning lol. So on a fresh turn on for the day, the left side speaker doesn't hum until about 5-10 seconds after the reel deck is turned on. Once it starts it is a pretty loud buzzy hum that sound is constant (meaning it does not gradually build in sound, the hum appears and does not change for the duration of the reel deck being on). It's hum is the same volume as the music that is being played The right side takes time to build. For about a minute there is no hum, it gradually builds louder and louder until a point where it is almost as loud as the music being played.

I will try pulling out the tubes today. Should I try and do all the tubes, or just the pre amp and output? There are 2 AF amp tubes as well 1 bias osc tube.

If I understand the last question correctly, it is coming from the speakers. I can change the volume on the reel to reel and the hums increase in the speakers.

AllanJ, I do not fully understand that statement so I will stay away from that method for now. If it comes down to something like that, I will have a professional take a look at it. Thank you for the suggestion though
 
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Old 08-21-18, 11:06 AM
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OK, learning more here. YES, you should be able to remove even HOT/ON tubes, one at a time, using an oven mitt, without doing damage, usually.

60 Hz speaker hum could be caused by a heater to cathode short inside a tube. 120Hz speaker hum usually caused by these filter caps you have already been working with.

If you think of this tape deck as having two independent channels, Left and Right, with each having a preamp (feeds from the tape head), then progressively more gain/power as you move towards the speaker, then you can apply more logic to the problem(s). BUT, there are some common circuits, L/R, such as the power supply, and the bias oscillator, as examples.
Don't forget that this unit likely also has a record capability, if it has mic inputs, or LINE inputs.
Without a full model number and schematic in front of me, I hesitate to analyze any deeper.

BUT, also look for any tube with slowly glowing red PLATES. That is bad, and indicates a different type of capacitor that has become leaky (commonly, but not only).

Does your tape deck drive speakers directly?? Or, are you listening with a headset?
 
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Old 08-21-18, 11:26 AM
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Awesome, shortly will be taking the tubes out and will have more info on glowing and hum reduction. I am also going to recheck my solder work and make sure there aren't any potential shorts in both the cans I replaced. It does have record capability so it does have line in.

The reel deck is a Wollensak T-1580 and here is the schematic if you wanted to take a deeper look

The deck is ran into a Denon AVR-1312 receiver and also has a set of speakers inside the machine, both display the same issues.
 
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Old 08-21-18, 11:48 AM
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schematic helps tremendously.
If there is hum even when volume is all the down, then later stages are suspect.
If hum goes away with volume down, then look to V1 and V4 stages.
You noticed the four adjustments for HUM in the pre-amp stages?
 
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Old 08-21-18, 12:02 PM
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I have tried adjusting with the hum adjustments, no change across the board on both channels. I tried that last night actually just as an easy test. I have replaced the V4 when I first got it when it didn't play any sound, which could make sense why I am not having too much hum out of the right channel if it is in fact a plethora of tube issues.

I just made sure that it does not have a hum on both channels when the volume is turned down on the reel deck. The original V4 I took out sounds like it has some pieces of metal floating around in their if I give it a shaking. I still have it just in case, but I suspect it was malfunctioning if it rattled (using light bulb logic with this one, so not sure if my assumption is 100% correct)
 
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Old 08-21-18, 04:07 PM
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UPDATE: I have taken most of the tubes out and even switched them around a bit to see what would happen. Results doesn't seem to be a good sign for me

V1 taken out caused no sound out of its corresponding speaker
V4 taken out caused no sound out of its corresponding speaker
V4 slot switched with V1 tube made no difference in hum
V5 taken out caused no sound out of its corresponding speaker
V7 taken out caused no sound out of its corresponding speaker

I am unable to get the output tubes (7591) out. They do not want to seem to budge with the wiggle technique. Am I missing something about these tubes that I have to do to get them out, or just keep trying to wiggle them out?
 
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Old 08-21-18, 04:50 PM
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This tells me that the hum starts upstream of V5/7. Without test equipment, this takes us to allenJ suggestion of brief shorting the grid to cathode of V1, V4 to see if that kills the hum.
You will have to be very careful. If the plate is picked accidently, bad things will happen.
TUBE GEAR; hard to kill it, but it can kill you.
MODERN GEAR; easier to kill, but is much safer to work on.

Strongly advise to check DC voltages with a DMM to verify what pin is what. Sams photofact has, I think, normal pin volages listed.

C3, C5 are suspects too. Maybe the last of the electrolytics in the set. Low $ too.
 

Last edited by telecom guy; 08-21-18 at 05:19 PM.
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Old 08-22-18, 10:32 AM
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I am not too sure if I want to venture into shorting the grid to cathode honestly. I can't find much information on how to do it and what it even entails doing. I am new to all this so without a detailed guide on exactly what do do, I could do more damage than good. If anyone has something along those lines, I will gladly look and research and reevaluate, but at this time it makes me unnerved to mess with the electricity paths.

2 things, I will most likely try and replace the C3 and C5, but why is it those specifically and not the other electrolytic capacitors? Second, could these problems be a result of a shotty solder job on these new cans? I will honestly say that I am a beginner at best at soldering but would happily detach and resolder if that could be a possible issue. Can post pictures here as well if that will help determine that
 
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Old 08-22-18, 11:11 AM
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Those preamp stages are not particularly dangerous. UNLIKE the 7591 tube area, which is fed with a highish power 280V dc source. That will light you up pretty good! maybe forever....
C3 and C5 i see have an interesting job bypassing the very low level input signal shield. Definitely replace those, and make sure the NEG ends of all the other caps you replaced are well soldered to the chassis. Need a hot iron for this. Lots of unwanted ac ripple on the DC lines will cause hum.
 
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Old 08-22-18, 11:15 AM
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Fix Up that Old Radio! | Nuts & Volts Magazine

some good safety info in there for tube gear.
 
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Old 08-23-18, 09:38 AM
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Thanks for that link, I will give it a good read! I will be buying C3 and C5 replacements on payday. I will update once I have them switched out and go from there. Thank you for the help and suggestions, always greatly appreciated!
 
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