GRETSCH 1962 6161 COMBO - INFO & ADVICE NEEDED

[ngw]

Hi all,

I have been brought a GRETSCH 6161 Combo to check over and to advise the owner what needs to be done to make it work properly.
The owner bought it in the USA and he says it works, but at very low volume.

This amp is very original by the looks of it, but I have never seen one before, as Gretsch amps are rare in Australia.
It still has a USA PT and the owner supplied his step-down transformer, to drop down from 240VAC in Oz.
I have not turned this amp on yet.
I am concerned that it still has the 2 wire power cord; and probably a death cap still connected.

I need some advice on the best way to approach working on this amp, as the owner wants to keep it original; this means not changing to modern components; and probably not fitting a safe 3 wire power cord, although I haven't clarified this yet.
What would your advice be, regarding the 2 wire power cord and the step-down transformer.
If any of you have any experience with these Vintage Valco/GRETSCH amps and can give me some advice, I would very much appreciate your help.

Pictures attached.
Cheers, Noel.

GRETSCH 6161-INSIDE RHS.JPG

GRETSCH 6161-INSIDE LHS.JPG

GRETSCH 6161. IMG_3665.JPG

GRETSCH 6161- MODEL NUMBER.JPG

[sluckey]

Disconnect C1. Then just secure your earth ground wire to the amp chassis at some convenient screw. It'll be safe.

https://el34world.com/charts/Schematics ... h_6161.pdf

[xtian]

Hi! Amp looks to be in great shape. You should be able to get it running nicely.

Here is a schematic for our discussion: https://el34world.com/charts/Schematics ... h_6161.pdf

C1 qualifies as a death cap (hot or neutral to chassis) and I can see it connecting your fuse holder to chassis--clip this out.

Yes, DEFINITELY install a 3-prong power cable, and securely bond the earth connection to the chassis. Also confirm that, when plugged into his voltage transformer, that the chassis is still properly earthed. No amp should ever leave your shop unearthed.

It's very likely you'll need to replace the electrolytic caps. I would do it as a matter of course--regular maintenance like changing the oil in your car. It will make the amp SO much happier. I see that this amp is severely under filtered. Do you see that the B1 DC node feeds SIX triodes? Usually TWO is the most we prefer, FOUR if it's a vintage Fender or whatever. So I'd add another node to feed V1 and V3.

Finally, it's pretty common for vintage amps to run hot here in the US, because they were created when home service was 110v, and now it's 120v or higher (123v right now at my house). So it's a good idea to cool the power tubes a little by changing that 250R cathode resistor to 300-360R. (The cathode bypass cap there is also an electrolytic, and should be replaced).

[Stevem]

Hi!

Dont concern yourself right now with changing over to a 3 wire grounded AC input, or changing out the output section cathode resistor, lets get the amp troubled shooted first!

In terms of those 6973 output tubes they can together produce over 25 watts and I am quite sure that with that amps very dinky output transformer which is mounted on that one oval speaker that the amp is not even capable of outputting even 15 watts , so those output tubes are not idling too hot even if the amp is getting 125 volts AC applied to it!

I see where the wires feeding the speakers have been cut into for testing I guess, so the first thing I would do is unsolder the wires on each driver and then jump a 9 volt battery across each driver and make sure they work.

Next on the list I would want to find out if the output transformer is shorted or open or not.

The best way to do this is to pull each output tube out one at a time and see if the volume output you do hear gets cut in half, or if you Basically loose it all together when just one output tube is in the amp.

If you loose it all together then take the other output tube and try it in that socket.
If it then basically stays cut out then the output transformer is shorted and must get replaced.

If the output transformer is open on one side the test out is easy as pin 9 connecting the tubes plate on its socket will not read a high DC voltage, but a low negative voltage.

It’s best to do these check outs with a 1K test tone into the amp of no more then 150 mv .
This input drive signal is a AC voltage and can be checked on your voltmeter.

[ngw]

Thanks for the response, sluckey and xtian and Stevem.

I told the owner I wasn't very happy about the death cap and having to poke around in a potentially dangerous old amp.
He agreed and I clipped the death cap out and added a temporary earth wire from the chassis to the step-down transformer, as a precaution.

I spent some time today checking and testing things and got the amp working and it doesn't sound bad (or fabulous); but it's a good start.
I checked voltages and they are all in the ball park, although the 6973s have different anode voltages and the screens on both are higher voltage than the anodes.
Screens= 345V. Anodes= 338V & 325V. The cathode voltage is 20V. Therefore: a-s= 325 & a-k= 318 & 305. The 12AX7s have good voltages.
I have a new pair of RCA 6973 valves, so I will try them tomorrow.
It has been a long day and it is now after 11:30pm, so time to quit.
I will see what tomorrow brings.
Cheers

[ngw]

Here is the schematic.

Gretsch_6161.pdf

[Stevem]

You need to understand that having the so called death cap in or out of the amp ( unless it’s shorted) does not make you more vulnerable to shock when working on the amp.

You however are more likely to get a shock when the amp is plugged into another item of equipment, or if you are touching the chassis of the amp and the chassis of another item of gear.
Since I have played in live bands since the late 60s which is well before grounded ac cables when required I have been shocked by a Mic screen hundreds of times and lived to tell about it!
Is a 60 volt shock fun, no but it is extremely rare that it will kill you !

[Stevem]

You need to understand that having the so called death cap in or out of the amp ( unless it’s shorted) does not make you more vulnerable to shock when working just working on the amp itself!

You however are more likely to get a shock when the amp is plugged into another item of equipment, or if you are touching the chassis of the amp and the chassis of another item of gear that is out of phase AC wise to that amp.

Since I have played in live bands since the late 60s which is well before grounded ac cables when required I have been shocked by a Mic screen or touching the chassis of out of grounding phase equipment hundreds of times and lived to tell about it!

Is a 60 volt shock on the lips fun, no as you do see a flash in your mind, but it is extremely rare that it will kill you !

[ngw]

Stevem and the others,

You guys seem to have missed a vital part of my first post: I live in Australia and our wall voltage is 230-240VAC, so the risk of electrocution is much more deadly. We have had earth/ground pins for much longer than you Americans, so we are not used to dealing with death caps and non-earthed old amps on a regular basis; not to say they don't exist. The times that I have encountered this issue is with US amps and equipment (like my EICO VTVM).
I also have been in bands since the mid '60s and have known of musicians getting shocks. Fortunately, the only time it happened to me was with a faulty lead, which left me flat on my back on the night club stage.
I have always been very cautious and so far, after all these years, I have never been shocked while working on amps. I have had a few fireworks displays and a few exploding electros, but they haven't got me, yet
I feel a lot better, about working on the GRETSCH, now that the death cap is disconnected and the chassis has an earth lead, albeit temporary at this stage.
Trusting one's life to a crappy ceramic cap, is not my idea of safety and at my age, I don't need to lose any more brain cells from shock treatment.
I am going to encourage the owner to have a permanent earth lead installed, also.

I will do some more on this amp today (Saturday morning), when I get time from the other jobs and I will let you know what I find and how it works out.
Thanks for the support and contributions.
The Amp Garage is a great forum and knowledge source and I appreciate the willingness, of all you Techs, to share your comments, advice and knowledge; I'm sure all the members appreciate each others' help also.

[Stevem]

Sorry about the location slip up , if the step down transformer is also a isolation type then you and the owner are golden!

[ngw]

No worries; I figured that you had missed my location.
Yes, the step-down transformer is isolated and carries the earth connection from inlet to outlet, so all good.
Thanks for taking an interest Stevem.
Cheers, Noel

[Leo_Gnardo]

ngw, I believe your view that safety is priority #1 is not only valid but vital. Sure, I've survived lots of shocks, but also learned some expressions that erupt when such shocks happen including: "STONE THE CROWS!" Indeed it was Stone The Crows' (the band) guitarist that met his fatal shock on stage, with the crowd watching. Some way to get famous... You never know which shock will be your last, and that goes double in 240V powered areas. Advice to the contrary is irresponsible and thoughtless. Ten feet tall and bulletproof, tell us all about it when you're in your coffin.

FWIW yesterday I wired a grounded AC cable into a nearly mint 1952 Fender Pro, after removing its death cap. Go ahead disbelievers, throw your mud pies. The amp's new owner insisted and I agree. He wants to live shock-free and enjoy playing through his new prize for a long long time. As Mr Fuchs says "Got a problem with that?" Read on, if you dare.

Wiki has the Stone the Crows story: "Guitarist and co-founder Les Harvey was electrocuted onstage in front of a live audience at Swansea's Top Rank Suite in May 1972. Wires to the group's equipment were reportedly damaged by the audience and although the road crew attempted to repair the damage, they overlooked a loose ground wire. Harvey received a jolt of electricity as he reached for a microphone while his fingers touched the metal strings on his guitar. His body reportedly flew into the air and came to rest with his guitar in contact with the microphone stand. Bandmates who tried to rescue him reportedly got shocked themselves and it wasn't until someone kicked his guitar away that medical personnel were able to render aid. He was pronounced dead on arrival at the hospital."

You don't have to get right across the power line, a scant few milliamps especially across the chest can stop a person's heart, dead. Yes there are stories about death row prisoners that survived the electric chair, but don't count on being one of them, I'm sure it wasn't much fun no matter how you slice it. Yes, the Stone the Crows event was 40 years ago but electricity hasn't become magically safer since then. Even if people don't get killed, a shock can be counted to put musicians (or anyone else) into a bad mood instantly. I've seen rehearsals and live shows stopped dead in their tracks when a muso gets whacked, especially right on the lips. Be safe, not sorry. Over n out.

[xtian]

Yes yes to all of this! Re: my other thread on the widowmaker amp, how did the industry pump out so many of those student amps where the chassis is bonded to one leg of the AC service? Did no one die? Seem like the religious right would have jumped on that—"Rock music KILLS!"

[ngw]

Thanks for adding that Leo.
I've heard of blokes being killed in Australia too. The risk is enormous for guitarists, as in Les Harvey's case, because we often leave one hand on the guitar when touching other devices.

I have found that it adds very little time to a job, to take the extra safety steps and can't see any reason not to. Accidents/Incidents will happen and people will get hurt/killed, so why invite them and increase the risk.
My Father was an Engineer with Australia's main Telco and he always said that prevention was always cheaper and better than the cure and when I started, as a Trainee Tech, with the same Telco in 1970, we were taught that we always had to practice preventative maintenance, because the cost of repair was too high and we would be held responsible for failures, due to our negligence, if we didn't adopt the correct procedure. We also had to adopt safe work practice, due to the high current levels and high voltage in some of the equipment, which would harm us and others.
I also raced motorcycles and bad maintenance and dodgy work, in that arena, very often cause serious injury and sometimes fatalities.
Mistakes happen, despite the best work practice, so there's no reason to cause them, with bad work practice.
As Leo said; It is better to be safe than sorry.

As xtian has added. It beggars belief that anyone would produce amps like that. Greed!!! Or they were trying to kill off the next generation of guitarists, playing that evil Rock music.
It was interesting growing up in that era when zealots proclaimed that Rock music was from the devil and should be banned. All music, including Rock, is actually a gift from God and food for the soul; turn it up LOUD.

[Stevem]

I agree and I know about the history you posted, but my comment started out with just the possibility of getting a AC shock while working on that amp before I ventured into my history of shocks.

To me the possibility of getting a fatal shock while working on a tube amp stems far more from all the high DC voltage points in a tube amp then the AC points you can come in contact with at least in terms of the county’s across the globe that are powered by 120 volt sources .

I have been shocked many times by the 22,000 or more volts sitting on cathode ray type color or black & white TVs picture tube of old, but the crater I still have to this day have in one of my fingers from a shock given to me by the 1.5 amps / 625 volts DC lurking in a Marshall Major amp will always be memorable

It seems you can release your body easier from being in contact with a AC source then a DC, at least that’s my observation!

At any rate safety is always paramount!