Disconnecting Speaker filed from the ciruit

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Studiogearlover

Well-known member
Joined
Mar 14, 2017
Messages
176
hey Guys

Theoretically,  can I disconnect the speaker filed (see schematic) as I wish to use another permanent magnetic speaker at the output?

If I will disconnect that would the 16uf+16uf filter capacitor be just a single 32 or 47 uf one instead?

Thanks for your help!
 

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I haven't seen one of those in the last half century.  You need to keep the speaker's field connected, it a major part of the DC supply.  But you don't need to send audio signal to the voice coil.
 
Speedskater said:
I haven't seen one of those in the last half century.  You need to keep the speaker's field connected, it a major part of the DC supply.  But you don't need to send audio signal to the voice coil.

Thanks Kevin, I see. Can I not remove that speaker at all?  I don't mind leaving that in but wondered if it is needed there if I am using with another speaker...  but reading your note as it is a "major part of the DC supply" then I guess should be always there...

 
The field  coil in the speaker forms a filter  between the two caps ,
A 10hy choke with the appropriate current rating should do the job nicely , if the caps are really old they might be paper in oil ,which as long as they arent leaking or overheating might well be good , there might be a benefit to adding some extra capacitance after the choke in the form of a modern compact electrolytic , you could probably mount it on the terminals of the existing cap easily.
 
Tubetec said:
The field  coil in the speaker forms a filter  between the two caps ,
A 10hy choke with the appropriate current rating should do the job nicely , if the caps are really old they might be paper in oil ,which as long as they arent leaking or overheating might well be good , there might be a benefit to adding some extra capacitance after the choke in the form of a modern compact electrolytic , you could probably mount it on the terminals of the existing cap easily.

Thanks for this!

It is electrolytic, but I am about to change... there is some hum there and unsure these are the tubes or the filter cap's. That 16+16uf is the original Sprague one from the 1940s....it is not leaking but better to change that i guess... would a 10Hy 60Ma 415Ohms  +/- 10% be sufficient ?

:)
 
60 ma might be a little on the low side , I havent seen the full schematic , so its hard to know ,
Most likely if its a power amp , a pair of tubes in push pull it could easily draw 60ma , then you need to take account of the ac current in the choke on top of that  . Either way your going to be using a sizable chunk of iron , if your drawing 60 ma dc in the circuit Id aim for a choke than can handle 90-120 ma , keeping it in and around the 600ohms dc same as field coil will help ensure conditions remain as they were inside the amp .

Theres all kinds of hidden pitfalls with the above , not least of which is finding a location for the new smoothing choke on an existing chassis , proximity and orientation of the choke in relation to the power transformer can cause unwanted interations so beware . As previously mentioned you can increase the value of the cap post choke/resistor but be sure to keep the  first filter cap after the rectifier close enough to the original value  otherwise your voltages will be off a signifigant amount and you risk damaging the rectifier tube . 

Please also remember if your new to this , Electrolytics can store charge for days after being powered off .
If your going to probe an energised tube circuit you dont want the typical uninsulated probe tips usually found on multimeters , at very least add some extra insulation so only the very tip of the probe is exposed , a crocodile clip on the negative lead  is best , then probe one handed , do Not make contact with chassis with your other hand .

 
Tubetec said:
60 ma might be a little on the low side , I havent seen the full schematic , so its hard to know ,
Most likely if its a power amp , a pair of tubes in push pull it could easily draw 60ma , then you need to take account of the ac current in the choke on top of that  . Either way your going to be using a sizable chunk of iron , if your drawing 60 ma dc in the circuit Id aim for a choke than can handle 90-120 ma , keeping it in and around the 600ohms dc same as field coil will help ensure conditions remain as they were inside the amp .

Theres all kinds of hidden pitfalls with the above , not least of which is finding a location for the new smoothing choke on an existing chassis , proximity and orientation of the choke in relation to the power transformer can cause unwanted interations so beware . As previously mentioned you can increase the value of the cap post choke/resistor but be sure to keep the  first filter cap after the rectifier close enough to the original value  otherwise your voltages will be off a signifigant amount and you risk damaging the rectifier tube . 

Please also remember if your new to this , Electrolytics can store charge for days after being powered off .
If your going to probe an energised tube circuit you dont want the typical uninsulated probe tips usually found on multimeters , at very least add some extra insulation so only the very tip of the probe is exposed , a crocodile clip on the negative lead  is best , then probe one handed , do Not make contact with chassis with your other hand .


Thanks. I will probably keep the speaker in for now. It is a 6v6GT output and the secondary on the transforemer is about 300-0-300 or 290-0-290 around 65 or 70 mA...

22uF capacitor can be used? or that is not so close enough to 15uF?

I could get hold of a choke mentioned in the previous post,  but that would not be sufficient i think. I will check with the new caps what is going on and report back.

Thanks for your help !
 
22uF should be ok , but just to be sure check the maximum value recomended for the rectifier tube ,

https://frank.pocnet.net/sheets/127/5/5W4.pdf

in the small print marked A    ,40uf is the max directly after the rectifier , otherwise extra resistance is needed ,
make a note of the dc voltages with the old components , when you have the new capacitors in place check again just to make sure the voltages agree with the schematic reasonably well , + or - 10% of the stated values will be fine normally .

Some interesting extra info here from PRR back in the day ,

https://el34world.com/Forum/index.php?topic=16366.0


 
Tubetec said:
22uF should be ok , but just to be sure check the maximum value recomended for the rectifier tube ,

https://frank.pocnet.net/sheets/127/5/5W4.pdf

in the small print marked A    ,40uf is the max after the rectifier , otherwise extra resistance is needed ,
make a note of the dc voltages with the old components , when you have the new capacitors in place check again just to make sure the voltages agree with the schematic reasonably well , + or - 10% of the stated values will be fine normally .

Thanks, will do so.

Actually, checking the rectifier tube in the unit it is a 5y3... I did check on the spec's of the 5y3's and the input is 20uf for capacitor. Looks like  22uF should be alright ..

many thanks for your help!
 
> check the maximum value recomended for the rectifier tube

There's no maximum cap on the 5W3 sheet you cite. The "Typical" assumes 25 Ohms in the PT winding, with a note that if the cap is >40uFd more impedance (Ohms) may be needed. With several K of series resistance the 5W3 would charge a 1 FARAD cap (still charging after an hour.......)

But with a Pi filter and a hollow rectifier, it makes some sense to leave the first cap at "traditional size", 4uFd-32uFd. Then some hundreds of Ohms or several Henries, and then go modern (BIG) with the second cap to kill the hum/buzz.

Since the original FC winding is clearly marked 600 Ohms, you want a replacement choke to be similar Ohms to get the design DC voltage. If a 415r choke is in-hand or nearby, use it with another 185r (150r, 220r) resistor in series. A single 6V6 plus little tubes will not exceed 60mA, but I would not fret even 2-6V6 at 80mA since the choke "limit" is to get rated inductance, not that it will burn-up. 10H is ample and if it falls to 7H@80mA it's still plenty, since the cost of 50 or even 500 uFd after it is so very small today.
 
PRR said:
> check the maximum value recomended for the rectifier tube

There's no maximum cap on the 5W3 sheet you cite. The "Typical" assumes 25 Ohms in the PT winding, with a note that if the cap is >40uFd more impedance (Ohms) may be needed. With several K of series resistance the 5W3 would charge a 1 FARAD cap (still charging after an hour.......)

But with a Pi filter and a hollow rectifier, it makes some sense to leave the first cap at "traditional size", 4uFd-32uFd. Then some hundreds of Ohms or several Henries, and then go modern (BIG) with the second cap to kill the hum/buzz.

Since the original FC winding is clearly marked 600 Ohms, you want a replacement choke to be similar Ohms to get the design DC voltage. If a 415r choke is in-hand or nearby, use it with another 185r (150r, 220r) resistor in series. A single 6V6 plus little tubes will not exceed 60mA, but I would not fret even 2-6V6 at 80mA since the choke "limit" is to get rated inductance, not that it will burn-up. 10H is ample and if it falls to 7H@80mA it's still plenty, since the cost of 50 or even 500 uFd after it is so very small today.

Roger that. Thank you.

How far can I go with the 2nd cap? i have few hundreds or uF's.. ? and is it worth it to change/remove the field coil speaker to reduce the hum with another coil or resistor or does not make any difference at all... meaning will I have the same results just increasing the 2nd cap size? If yes, I would just leave that speaker in but if it will do a better sound/ less hum with a choke...might swap that ...

Thanks for your advise.

:)
 
I think it all depends on what your using it for ,
We didnt see the rest of the schematic so we dont know .

A single ended output stage requires much lower noise in the plate supply than a push pull amp , this is because sources of psu noise in a push pull amp  add together out of phase in the transformer and so cancel to a great extent , this cancellation doesnt occur in a SE topology .

Ive gone to the trouble of reducing  noise in power hungry single ended tube stages passively ,its not a trivial exercise .
Double pi with two chokes ,470 or 680uf  caps and excelent layout will get it low , but at some point magnetically induced noise from the mains transformer will end up in the output  transformer and adding extra filtering after that doesnt make much difference  ,  layout is the only real way to improve things from there , that might include ,sheilding or screening or even moving the mains transformer onto its own separate chassis .
 
Tubetec said:
I think it all depends on what your using it for ,
We didnt see the rest of the schematic so we dont know .

A single ended output stage requires much lower noise in the plate supply than a push pull amp , this is because sources of psu noise in a push pull amp  add together out of phase in the transformer and so cancel to a great extent , this cancellation doesnt occur in a SE topology .

Ive gone to the trouble of reducing  noise in power hungry single ended tube stages passively ,its not a trivial exercise .
Double pi with two chokes ,470 or 680uf  caps and excelent layout will get it low , but at some point magnetically induced noise from the mains transformer will end up in the output  transformer and adding extra filtering after that doesnt make much difference  ,  layout is the only real way to improve things from there , that might include ,sheilding or screening or even moving the mains transformer onto its own separate chassis .

I see... attached the schematics in full.

So shall I leave that field coil in and try with the second cap lets say 500uF or so after the field coil and hear the results? Would that reduce the hum? the speaker is not near the power transformer and not near to the output transformer either...

 

Attachments

  • meissner_mfg_div_maguire_industries_inc_brewster_9_1065_pg16-1.png
    meissner_mfg_div_maguire_industries_inc_brewster_9_1065_pg16-1.png
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> Would that reduce the hum?

A 33uFd-500r-100uFd Pi filter usually makes a Champ (what this is) "totally free" of B+ buzz and suitable for small-room recording. 500uFd after 600r seems like building a dog-porch out of 2 feet of concrete, over-kill.

Hum/buzz is an onion, layers. When the B+ is clean the heater wiring hums (you may want to change the one-side-grounded heating). Preamp on the same chassis with power transformer always hums some. I bet this is a guitar-amp project and all *guitars* in powered rooms pick up much hum/buzz.
 
PRR said:
> Would that reduce the hum?

A 33uFd-500r-100uFd Pi filter usually makes a Champ (what this is) "totally free" of B+ buzz and suitable for small-room recording. 500uFd after 600r seems like building a dog-porch out of 2 feet of concrete, over-kill.

Hum/buzz is an onion, layers. When the B+ is clean the heater wiring hums (you may want to change the one-side-grounded heating). Preamp on the same chassis with power transformer always hums some. I bet this is a guitar-amp project and all *guitars* in powered rooms pick up much hum/buzz.

Thanks

So far what I have installed is a 16uf first filter cap and keeping the speaker field coil...for the second filter cap, just wondering of some massive cans I have of 200uF. These are 275V DC WKG/ 350V Surge. I know I am pushing this but probably will have around 245-250 VDC after the coil. Would this be a good idea? These are really good quality massive caps....i know on the schematic the voltages are 450VDC , however if this would work, would do a great job I think.,.
 

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