geloso g1/1110-a ppimv

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geloso g1/1110-a ppimv

Postby hobbits on Wed May 20, 2015 10:10 am

Dear All,

Since last Saturday I'm in possession of a Geloso 1110. It is in a very good condition (mint). The original capacitors are in place and working.

interior..
Image
Mint isn' t it?
Image


This powerful amplifier really needs master volume. I have read a lot about the ppimv and i think this will be the right solution. But where to place this and what to replace?. Could someone here help me?

scheme:
Image

Things i did already:

-installed a " bleed resistor"
-replaced the voltage supply cable with a decent euro cable with earth
-removed the death caps.

Thanks for sharing your knowledge.
hobbits
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Re: geloso g1/1110-a ppimv

Postby Racing on Fri May 22, 2015 10:56 am

Sure can.

First up,make sure you´ve got the right schematic. There were two revisions of that amp.

PPIMV.
The ECC81´s latter part shows that there is equally large resistors for the plate and cathode side of that triode. That there is a concertina/cathodyne phaseinverter.
Outbound of that,following the schematic,there´s a pair of 100nF caps (0,1uF). One for each side of the powerstage. One from the plate side of said ECC-81 and one from the cathode side.

What you need to do is install yet a pair of 100nF caps and a "twin" pot. Ie; a dualgang pot of 2*500k log for instance.

You disconnect the side of the stock 100nF caps heading for the powertubes and route the signal from there to the inbound side of the dualgang pot. The route the signal from the wiper of each pot back towards the powertubes. It´s just that where the signal hits each powertube "rail" you install one 100nF cap. One for each side.
This way you use them coupling caps to make sure that no DC voltage reaches the pot,which is essential.

There are a few other ways of handling this,but TBH what´s described above works and works very very well.

Lemme know if it checks out for u.
Racing
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Re: geloso g1/1110-a ppimv

Postby hobbits on Fri May 22, 2015 11:26 am

Racing great answer. I have to get the parts first and will let you know how it turns out. Would those new caps also be 1000V?
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Re: geloso g1/1110-a ppimv

Postby Racing on Sun May 24, 2015 11:16 am

No need what so ever.

The side heading for the PI sees like maximum 400V no matter what and the other side in turn,the one heading for the powertubes,like minus 40 max. I commonly use 630V ones all over. That way...better safe then sorry-sorta-and it keeps amount of spares on the shelves down.
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Re: geloso g1/1110-a ppimv

Postby hobbits on Thu May 28, 2015 7:09 am

Yesterday I built in the ppimv. I placed the 2 extra capacitors and just in between I placed the dual potentiometer of 500K (log).

I am now able to use the pre volume as gain, the ppimv gives a nice control on the overall volume.

Thanks for the help. :jam:
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Re: geloso g1/1110-a ppimv

Postby Vortexion on Thu May 28, 2015 8:44 am

Nothing useful or clever to add to this thread. Just called in to say what a LOVELY amp that is! 8)
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Re: geloso g1/1110-a ppimv

Postby Racing on Thu May 28, 2015 12:26 pm

@Hobbits.
Here´s a few extra trix for ya then.

First up. Get rid of all that nonense that isn´t used between stage 1 and 2. The added pots and what have you not...outta there. Reason is that it works as a second voltage divider and hence robs you of gain (read-amplification).
Second up......
The last triode in the schematic is the concertina phaseinverter. The stage before the concertina is called its driver. The two are AC coupled together only. The involved 100nF cap between the driver and the grid of the concertina is overkill beyond belief. Do the math...(there´s calculators for this online. RC nets). Bring that 100nF value down. Considerably. I´d say..4,7nF does it. (That value will still be ample for for instance bass work)
Ontop of that..the signal heading for the grid of the concertina needs a sizeable gridstopper. Install a 470k resistor right at the grid of the concertina and report back.
What it´ll do is get rid of that "icepick" behavior that a concertina normally brings.
In turn..the concertina carries a cathode resistor that is decoupled by a 50uF electrolytic cap. Remove the cap completely and reset the resistor to like 3,3k.
This´ll warm the tone up for ya.


Tonestack in turn. This isn´t a tonestack at all,it is a James network. The James network,once you understand how it works and why,is IMO a WAY more viable setup then any of the "regular" stacks will ever be.
For more mid oriented guitarwork it needs to be reset a bit tho. The thing here is that you can basically tailor a James to hearts desire by altering the values of the components involved.
Most regular Fender/Marshall et al stacks are midscooped from the onset. The Fender type more so then the Marshall and herein lies much of the trick of the tone of an amp.
The James can be setup to be completely flat in "zero" position for instance,and for guitarwork..that isn´t sans merit. The guitar is by any measure a midoriented instrument,just that midfocus of the guitar shifts with being clean vs distorted,and this needs to be accounted for.

If distortion is the name of the gamle try the following...

Inbound for treble=680pF cap. Ceramic works just fine while evaluating.
Inbound for bass=100k resistor.
Outbound for treble=2,2nF vs ground
Outbound for bass=3,3nF heading into a 10k resistor vs ground.
Separation resistor= 220k.

Try that on for size and see what ya think. If you haven´t already download TSC (tonestack calculator). There´s a heading in there called James,and there you can iterate to hearts desire. Do NOT go faint on particular looks of a given setup. Try ´em for size FIRST. My guess is that you´ll touch down around the values above.
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Re: geloso g1/1110-a ppimv

Postby hobbits on Tue Jun 02, 2015 1:28 pm

Thanks racing for your tips.

I already played around with the james network and added a mid boost by placing a parallel capacitor around the treble capacitor.

like (not my setup but for the idea): Image

And i'm experimenting with the negative feedback for a presence control.

For now i' m satisfied with how it sounds. I did 4 rehearsals and a gig with it. Maybe in the future i will experiment on whit the help of your tips.

Image
Image

More to follow..
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Re: geloso g1/1110-a ppimv

Postby hobbits on Tue Jun 02, 2015 6:11 pm

cabinet finished:

Image

Image
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Re: geloso g1/1110-a ppimv

Postby hobbits on Tue Jun 02, 2015 8:38 pm

Is this what you mean Racing?

Image

Did you experiment with the negative feedback?
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Re: geloso g1/1110-a ppimv

Postby Racing on Tue Jun 02, 2015 9:45 pm

Yep.
That´s about it. Of course you can go heaps further,but suffice for now that...them mods alone will make that amp into way more of a guitar ditto.

I´m 100% with you in that the amp is so powerful that it NEEDS some means of controlling volume,and in my case (as yours) that has been through the implement of a PPIMV.
Now. That also brings that any and all NFB circuit will be largely affected. As the PPIMV in essence controls volume output and hence the signal sent to the speakers via the output transformer that also bring that any and all functions run by said negative feedback will be too. Ie; a lot LESS signal will be available as volume is turned down.
Hence..i these days set that stuff up accordingly (for instance look into various Hiwatt designs).

That is not to say that a presence setup will be sans effect. It is to say that to get repeatable work out of said circuitry you need to reassess.
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Re: geloso g1/1110-a ppimv

Postby hobbits on Wed Jun 03, 2015 3:26 pm

Thanks again Racing you made me a very happy geloso owner. I will report back if a change things or have other update' s

greetings Peter
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Re: geloso g1/1110-a ppimv

Postby hobbits on Tue Jun 09, 2015 8:15 pm

I was testing the amp with some different tubes. Because i experienced 50 hz hum. I replaced all of the preamp tubes and 2 of the el503. When i turned the amp on, the 5 ohm 2watt resistor (cathode resistor? it' s on the el503) got burned and one of the tubes sparkled. Damn..

I can' t find any shorts. Could it be one off the power capacitors?. Just before the tube replacement the amp was working but with a lot of 50Hz hum.

I hope the el503 tube is still working.

burned resistor:
Image


fuse?:
Image
Last edited by hobbits on Wed Jun 10, 2015 6:35 am, edited 1 time in total.
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Re: geloso g1/1110-a ppimv

Postby Racing on Wed Jun 10, 2015 2:59 am

If 50Hz that means that we´re talking raw AC voltage. If it originates after rectification we´re talking 100Hz.
Big difference.

The only real viable solution for checking/testing e-lytes that i know of is an ESR meter. If you don´t own one it is likely that your electronic parts vendor does and can test the caps in case for you.
First thing up is to check physical integrity of the e-lytes. Ie;that both leading legs of each cap is still attached.

Then again...
If you get appreciable amounts of 100Hz hum that should also show in AC form with the amp up and running at the first hit electrolyte. To be blunt the onboard caps are old by any measure today and should at least IMO be replaced,if we´re talking an amp that is to see regular service.
Anyways.
Seing the involved capacitance you should see no more then approx ~5VAC at the first hit electrolyte. Ie; the electrolyte that is the first one to see voltage after rectification is done. If that value is up by much=shot e-lyte,and in that case to be safe..replace all of them.

In doesn´t HAVE to be the e-lytes tho. 100Hz hum can for instance also develop within the powerstage too as you´ve got powertubes that goes way out of balance. Each side of that push/pull stage should idle at about the same total number. This is one of the reasons why i for one am an advocate of installing simple 1 Ohm/1w resistors between the powertube sockets and ground for each and everyone of the sockets in case.
Reason is simple..
That way it becomes real easy to swiftly assess if each involved powertube is doing its job. Each and every one of them should pull its approx same weight vs the output transformer under load in idle.

IF we´re really talking 50Hz hum (as in mains socket 50Hz) then the first thing to suspect would be the heater circuit of the amp. The "high voltage" end of the amp is limited to say the least. Ie;the area it will affect within the amp is limited to the proximity of the mains switch and the power transformer and hence..it is way unlikely that it´s presence would alter much and hence in turn...change the name of the game.
Way to check ground reference for the heater circuit is by measuring voltage between each "side" of the heaters where it hits a socket and ground. Then check total voltage by checking between the leading legs of the circuit. Voltage vs ground should be approx half of the total.

However...as it has DEVELOPED a hum the most likely scenario is that one of the powertubes has malfunctioned. Ergo a surefire and simple means of making sure is the install of them 1 Ohm/1w resistors between each powertube socket and ground,and here´s the deal....

Ohms first law states that;
U=R*I
Where U is volts,R is resistance in Ohms and I is amperage in Amps. Now...if we set R=1 that brings that we can toss and turn in that formula and end up with the fact that the measured voltage drop across that resistor can be directly translated from mV to mA.
...keep that thought....´cause...

Ohms second law states that;
P=U*I
Where P is wattage in watts...rest per above. Right. So we now KNOW the actual mA drawn across that 1 Ohm resistor. Ok?
Next up we measure the actual B+ voltage. Ie; the highest voltage the powertransformer provides us after rectification under load in idle....and we put that into that equation.

For instance. We see a voltage drop across that 1 Ohm resistor of 40mV in idle. No load. Ok.... We then measure B+ to be 400VDC.
The 40mV can be directly translated to 40mA...

Ergo. 400*0,04=16. That tube pulls 16 watts anode loss in idle. We then look the datasheet up for the tube in Q...and the 503´s will state rather low power numbers vs what they can provide IRL...we STILL take them numbers into account-no matter.
Which brings that the tube in Q has a maximum rating of 24w (if memory serves me). 14/24=~58%. A rather cold set bias in other words. You normally set bias to between 65 and 85 percent,a little depending.
Later developed tubes,like the 503,in my experience "like" to be set rather hot. IOW...shoot for the 85 number.

I believe you by now am aware of how to set the thing up to have its fixed negative bias adjustable for amount. E regular trimpot yadda yadda... However implementing balance for the various powertubes become a bit more involved.
In that case...install the 1 Ohm resistors and be CERTAIN it is needed first..and we´ll take it from there.
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Re: geloso g1/1110-a ppimv

Postby hobbits on Wed Jun 10, 2015 8:23 pm

Racing,

You quick response is beyond my imagination. I will first learn my self a bit more about tube amp and i try to find somebody in the neighbourhood to help me with this problem.

I will certainly get this thing alive..

The tube which began to glow has a connection between the anode and cathode. Is this a cause or an effect?.
The fuse is bridged with a wire is that normal?.
could the spool - resistance and fuse be replaced with some thing?
What is the function of that little spool?

greetings P
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