# Crazy hum with pedal(s)



## Verne (Dec 29, 2018)

I have an old Pepco amp. 1964 I believe. It has a slight hum when just playing through the amp alone. Nothing that really drives me nuts as it isn't nearly as noticeable when playing. Once I try to add my entire pedal board, or even just one pedal, it becomes a very LOUD hum that is very annoying and to hear the guitar, the volume has to go really loud. The hum when pedal(s) are plugged in is actually louder than the normal volume I play at. It has not had any update mod. (or any mods for that matter) done to it. Straight up original. Not having the transformers, is this the major reason it hums? I don't pretend to understand electrics/electronics, so I am throwing out a guess. If this is inherent in this type of amp, I'll just play without pedals. Just wondering if it's something easily taken care of. Easy and inexpensive. I got the amp for a song, and throwing hundreds of dollars at it is not really my plan. Spending more to fix than it's worth doesn't seem logical. It's far from a collectors piece.


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## Budda (May 29, 2007)

Is it modded to 3-prong?


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## DaddyDog (Apr 21, 2017)

Try same power outlet. Try different power outlet. If a 2 prong cable, turn it around (to reverse polarity).


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## Verne (Dec 29, 2018)

Budda said:


> Is it modded to 3-prong?


No. As stated, entirely original with no mods. 



DaddyDog said:


> Try same power outlet. Try different power outlet. If a 2 prong cable, turn it around (to reverse polarity).


I will try all this later and report back.


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## TimH (Feb 4, 2006)

Verne said:


> No. As stated, entirely original with no mods.
> 
> 
> 
> I will try all this later and report back.


Try lifting the ground of one of your patch cables and using it to plug into the amp after effects.


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## Budda (May 29, 2007)

Get mike at vintage tonewheels to 3 prong it.


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## Lincoln (Jun 2, 2008)

It could probably use some new filter capacitors by now too.

It's probably just getting by as is, and a pedal added to the chain pushes it over the edge.


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## Paul Running (Apr 12, 2020)

Make sure every device has a good return to ground, use an ohmmeter to verify your grounds.


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## nonreverb (Sep 19, 2006)

Does the amp have a power transformer? If it's a direct voltage or voltage doubler design (no power transformer), it will be a nightmare as the amp's ground is the neutral...or hot. Also, if it is this type, best to get an isolation transformer installed for your safety....and the safety of your pedals.


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## Latole (Aug 11, 2020)

nonreverb said:


> Does the amp have a power transformer? If it's a direct voltage or voltage doubler design (no power transformer), it will be a nightmare as the amp's ground is the neutral...or hot. Also, if it is this type, best to get an isolation transformer installed for your safety....and the safety of your pedals.


*Op write ; " Not having the transformers, is this the major reason it hums?"*

100 % right, don't use it if amp don't have power transformer , very dangerous for you and for your pedal,
You may have 80 to 110 volt on chassis.
Picture of the amp please.
Wich tubes in the amps

These amps are called ; widow maker;








What is a widowmaker amplifier? — Tropical Fish


A widowmaker amplifier has no power transformer or fuse. Instead, the two-prong, non-polar power cord is wired directly to the rectifier tube. It is very unsafe, because under even minor failure conditions (such as a shorted capacitor or even - in some models - plugging the power cord in backwards),




www.tropicalfishvintage.com


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## dtsaudio (Apr 15, 2009)

You have a current path through your pedal board. There could be significant voltage on the chassis of the amp.
I cannot stress enough what others have mentioned. This amp needs a transformer installed, and a three prong power cord you are using a potential lethal weapon.


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## Lincoln (Jun 2, 2008)

This is an easy way to go if your pepco doesn't have a power transformer. Some do, some don't. If any of your tubes start with a "35" or "50" instead of a "6" or a "12" , you need an isolation transformer.

Hammond 171A


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## Verne (Dec 29, 2018)

I don't recall it having any transformers at all. From inside the amp. Took this when I first got it.


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## nonreverb (Sep 19, 2006)

Verne said:


> I don't recall it having any transformers at all. From inside the amp. Took this when I first got it.


Definitely no power transformer in there. 35Z5 and 50L6 is a dead giveaway. You need to have a isolation transformer installed before you proceed any further.


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## Latole (Aug 11, 2020)

nonreverb said:


> Definitely no power transformer in there. 35Z5 and 50L6 is a dead giveaway. You need to have a isolation transformer installed before you proceed any further.


I agree *don't use this amp until its mod,* you can hurt or kill yourself and damage your 
gear.
I have a amp close to yours with no Power Transformer.
I mod it with Isolation Transformer and 3 prong cord as I'm in electronic. Now it is safe.
I put new filter cap ( 2 blue caps at right ) and adjust bias.
I had few bypass caps ( blue caps at left) for a better tone. Now it is a great little amp, sound better than original.










Original circuit ;









Circuits with Isolation Transformer and 3 prongs cable


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## Latole (Aug 11, 2020)

Isolation transformer;


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## Verne (Dec 29, 2018)

Okay. I generally leave it plugged into a power bar with a separate power switch. I leave the amp in the on position and volume I like and never actually touch the amp because I use the power bar as the main switch. I did reverse the plug and the hum went back to normal levels. Well, as normal as they've been since I've gotten the amp. 

I will see about an isolation transformer and 3 prong. No way in hell I could do that as my electronics knowledge was limited to wiring and R/C car years ago.


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## Paul Running (Apr 12, 2020)

*WARNING: A tube amplifier chassis contains lethal high voltage even when unplugged--sometimes over 700 volts AC and 500 volts DC. If you have not been trained to work with high voltage then have an amp technician service your amp. Never touch the amplifier chassis with one hand while probing with the other hand because a lethal shock can run between your arms and stop your heart. Use just one hand when working on a powered amp.

WARNING: A tube amplifier chassis contains lethal high voltage even when unplugged--sometimes over 700 volts AC and 500 volts DC. If you have not been trained to work with high voltage then have an amp technician service your amp. Never touch the amplifier chassis with one hand while probing with the other hand because a lethal shock can run between your arms and stop your heart. Use just one hand when working on a powered amp. *


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## Latole (Aug 11, 2020)

Verne said:


> Okay. I generally leave it plugged into a power bar with a separate power switch. I leave the amp in the on position and volume I like and never actually touch the amp because I use the power bar as the main switch. I did reverse the plug and the hum went back to normal levels. Well, as normal as they've been since I've gotten the amp.
> 
> I will see about an isolation transformer and 3 prong. No way in hell I could do that as my electronics knowledge was limited to wiring and R/C car years ago.



Power bar is no more safe. You can do same if you unplug the amp power cord from the wall outlet.

To resume; don't use the amp anymore, your can destroy you gear/ pedal


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## nonreverb (Sep 19, 2006)

Verne said:


> Okay. I generally leave it plugged into a power bar with a separate power switch. I leave the amp in the on position and volume I like and never actually touch the amp because I use the power bar as the main switch. I did reverse the plug and the hum went back to normal levels. Well, as normal as they've been since I've gotten the amp.
> 
> I will see about an isolation transformer and 3 prong. No way in hell I could do that as my electronics knowledge was limited to wiring and R/C car years ago.


I get these in for repair occasionally and insist the customer have an isolation transformer installed or I will not work on it. It's that serious an issue.
It still mystifies me how CSA could approve these designs. Sure, they were fine for radios of the time with plastic/bakelite cases and knobs...the user was isolated from the chassis. Not so with guitar amps where the user becomes part of the 120VAC current path to anything resembling ground.


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## alwaysflat (Feb 14, 2016)

Latole said:


> I agree *don't use this amp until its mod,* you can hurt or kill yourself and damage your
> gear.
> I have a amp close to yours with no Power Transformer.
> I mod it with Isolation Transformer and 3 prong cord as I'm in electronic. Now it is safe.
> ...


Nice to see an original diagram that's made it to the 21st century. I'll be saving that one, thank you very much.
In my 50L6 version I've derated the tranny and gone with a larger Hammond, due to the 1/2 wave rectified B+ load. 
!/2 wave load is less significant, vs heaters, my choice was probably more a result of OCD


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## Latole (Aug 11, 2020)

You talk amp made 60 years ago. At time poeple drive their car and drinking their beer.....No seat belt, no air bag..


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## Budda (May 29, 2007)

Verne, hit up Mike.


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## Verne (Dec 29, 2018)

I had sent Mike an email not long ago, and was quoted $185 for 2 transformers, 3 prong and whatever else it might need. He also said it's an estimate and could go higher. To be honest, putting as much, if not more, money into it than it cost is not a goal. I'm not expecting to recoup money if I sold it, never have. Just not wanting to drop a lot into it. It sounds good, but it doesn't get used a crapload. Part of the appeal was the year of amp and my birth year are the same.


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## Latole (Aug 11, 2020)

Why 2 transformers ? One amp or two ? 

Working on low budget amp cost same price as a high end amp


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## Verne (Dec 29, 2018)

He told me an output transformer as well.


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## Latole (Aug 11, 2020)

Verne said:


> He told me an output transformer as well.


Why ? Your amp work, so it don't need O.T.


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## Latole (Aug 11, 2020)

Isolation transformer cost $20 plus shipping ($10 ? ) 3 prong cord $6 labour 1 hour ( $30-$40 ? ) 
Maximum $75 job
To bad you leave too far from my home, Il do the job for less


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## Verne (Dec 29, 2018)

If I knew electrics, I'd be on this, or it'd be done by now. I have a buddy who may be able to put one in for me. I have enough power cords from other amps and such that I won't need a new one, just wire one of these in. I won't use the amp until this is installed. Thanks guys.


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## Latole (Aug 11, 2020)

I use twice old razor wall outlet with isolation transformer like those one . I found them free or for cheap.


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## Verne (Dec 29, 2018)

I really am better off having somebody else source one for me. I am clueless to this stuff and could end up grabbing one that won't work. Whether off a site, or out of a wall.


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## Budda (May 29, 2007)

Given it's a safety hazard, I'd sell it.


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## dtsaudio (Apr 15, 2009)

Latole said:


> Isolation transformer cost $20 plus shipping ($10 ? ) 3 prong cord $6 labour 1 hour ( $30-$40 ? )
> Maximum $75 job
> To bad you leave too far from my home, Il do the job for less


On what planet are you getting your pricing from?
Transformer more like $40.00 unless you expect it to melt within an hour or so (like that wall transformer).
Maybe 1 hour labour, but more like 1 1/2 to 2, and I don't know a single tech that works for $30/hr.
Total job, probably around $150.00 as a fair price. There is a cost to a safe, professional job.


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## Latole (Aug 11, 2020)

dtsaudio said:


> On what planet are you getting your pricing from?
> Transformer more like $40.00 unless you expect it to melt within an hour or so (like that wall transformer).
> Maybe 1 hour labour, but more like 1 1/2 to 2, and I don't know a single tech that works for $30/hr.
> Total job, probably around $150.00 as a fair price. There is a cost to a safe, professional job.


Don't you follow post; my answer no 16 , $14 from Newark,
You are wrong about wall transformer, I use it on two amps. They are enough powerful.
I'm electronic tech, it is a beginner job, so easy.

I must admit I don't know amp tech market price, I never need to pay a electronic tech


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## dtsaudio (Apr 15, 2009)

Oksy, so it's $30.00 (with shiiping and tax). 
I still wouldn't use a pile crap i pulled out of a wall for a safety device.
And you're right it's not a big job, but you just don't throw something ad hoc together for a customer.
So I'll revise my price $120.00.


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## Paul Running (Apr 12, 2020)

Verne said:


> I am clueless to this stuff and could end up grabbing one that won't work.


The residential one in the photo is rated 20W...what is the mains power rating for your amp? If it's near 20W and higher, you are better off with a 50 watter...it will run cooler and you will be safer.


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## nonreverb (Sep 19, 2006)

dtsaudio said:


> Oksy, so it's $30.00 (with shiiping and tax).
> I still wouldn't use a pile crap i pulled out of a wall for a safety device.
> And you're right it's not a big job, but you just don't throw something ad hoc together for a customer.
> So I'll revise my price $120.00.


....and that's just to supply, mount and connect the transformer. That wouldn't include the essential replacement of the bad electrolytics and any other problematic components.


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## jb welder (Sep 14, 2010)

Latole said:


> I use twice old razor wall outlet with isolation transformer like those one . I found them free or for cheap.
> 
> 
> 
> View attachment 351777


That is a 20VA (approx. 20watt) unit, it is marked right on it. So approx. 200mA max.
Only for very small amplifiers, and I would use a 200mA fuse with it.

The Triad N68 unit you posted earlier is a much better choice at 50VA rating.
Like @alwaysflat mentioned above, with half wave rectifier it will run hotter than with full wave, so better to use over-rated just to be safe.


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## alwaysflat (Feb 14, 2016)

I went 60va via Hammond 169RS for mine after debating , a 201 chassis Pepco, and included bridge rectified dc to feed the 35Z5 , heaters are driven from in front of the bridge. Was a personal comfort thing to go 60va, its a keeper.


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## davetcan (Feb 27, 2006)

If it were me I'd still go with Mike at Vintage Tonewheels. He's the best amp tech by far that I've found locally. He's also always been reasonably priced. He's done quite a bit of work for me over the years and I've never had a single problem with anything he's done.


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## [email protected] (Feb 25, 2021)

Verne, that is not what I told you. What you've posted makes me sound incompetent, and possibly dishonest. My response to you, in its entirety, is copied below:

_You are right Verne, these amps are VERY dangerous in stock form. Definitely don't meet modern safety code.
I've done a bunch of these widow makers through the years. They usually need power supply caps replaced as well.
Cost would be in the $185 range for all parts and labour._

I have worked very hard, for a very long time, to earn a reputation for expert service and honesty, and I felt it was important to set the record straight here. Thank you.


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## nonreverb (Sep 19, 2006)

[email protected] said:


> Verne, that is not what I told you. What you've posted makes me sound incompetent, and possibly dishonest. My response to you, in its entirety, is copied below:
> 
> _You are right Verne, these amps are VERY dangerous in stock form. Definitely don't meet modern safety code.
> I've done a bunch of these widow makers through the years. They usually need power supply caps replaced as well.
> ...


On a different note, I'm surprised I don't know you as there are very few ready, willing and capable of handling Hammond/ Leslie repairs and service here in Ontario...let alone Canada.
Nice to know there are others as crazy as I am.


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## [email protected] (Feb 25, 2021)

nonreverb said:


> On a different note, I'm surprised I don't know you as there very few ready, willing and capable of handling Hammond/ Leslie repairs and service here in Ontario...let alone Canada.


Well ... I am half a province away from you. Honestly, 99.9% of my business is non-Hammond/Leslie now, but I'm still ready, willing and capable!


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## nonreverb (Sep 19, 2006)

[email protected] said:


> Well ... I am half a province away from you. Honestly, 99.9% of my business is non-Hammond/Leslie now, but I'm still ready, willing and capable!


I know a few guys in TO and Alex in Hamilton. It's always surprising when someone new pops up.
Yeah, Hammond biz right now is minimal....and the backline side is zero and looks to be that way for a while yet.
Diversity is the COVID key.


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## Verne (Dec 29, 2018)

@[email protected] I am sorry. I was going by memory and thought you advised it needed two transformers. Apologies if I misrepresented your response. I had looked in my emails and could not find your response. I have mistaken the caps needing replacement for the extra transformer. I don't know electronics and ask some very basic questions and mistake component names regularly. This is why I never touch anything but tubes in my amps. I won't even touch a solid state. 

The cost is what's preventing me from having the work done to it. It's a nice sounding little amp, but putting 2/3 the cost of the amp into work isn't in the cards at this time. I haven't used the amp since this thread started.

I had no intention of making anything sound derogatory toward you or your business. I regularly recommend you to tube related questions. I haven't had work done by you to this point, but your reputation proceeds you enough to forward your name any time I get asked to recommend.


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