geloso g1/1040 suggestions and wattage check

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Re: geloso g1/1040 suggestions and wattage check

Postby hobbits on Wed Dec 16, 2015 2:24 pm

Thanks for replying

Grid stoppers are replaced with new 5k6 resistors, like the jcm800. Sockets i've cleaned them out..
365 DC on the plates and a 25 volt ac as a signal.

I still think is is the OT. But I cannot just trow it away. So i'm still doing some testing with it.
Like in: http://www.geofex.com/ampdbug/outtrans.htm
the OT passes the simple tests and with the advanced tests i'm not so sure.

5 volt on the primairy gives me 0,56 volts on the secondary. But the other way around
5 volts (which drops to 2,3) on the secondary gives 38 (muts to low) on the primairy.

So i believe (not convinced) there is a load in the OT secondary side which causes a output voltage (volume) drop.
i'm already looking for a replacement. But 80 euro???for an amp i bought for 40
hobbits
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Re: geloso g1/1040 suggestions and wattage check

Postby Racing on Thu Dec 17, 2015 11:38 am

Sometimes shot OT´s can be real hard to pinpoint.
As you´re probably aware the wire used carries an enamel covering. If that enamel has gone AWOL in a few places it can be a real bitch to pinpoint.

OTOH when this happens you´ll usually react to that the amp works fine as you increase volume while as all of a sudden you reach a volume "roof" that sets the limit.
In worse case scearios it´ll pop the HT fuse so fast it´ll make your head spin.

You don´t have anyone around that can lend you an OT? Basically anything with a primary of 3-5k will do.
Racing
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Re: geloso g1/1040 suggestions and wattage check

Postby Racing on Thu Dec 17, 2015 11:39 am

Speaking of which.
NOS Geloso x-formers show up on Italian e-bay every now and then. Might be worth some consideration?
Racing
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Re: geloso g1/1040 suggestions and wattage check

Postby hobbits on Thu Dec 17, 2015 1:10 pm

Yee.., Im giving up on the OT. It was in a very bad condition all along.

But sinds the transformer is gone and i want this amp up and running. I am considering making a 5e3 / 5d3 fender of it. With two 6v6 and the new transformer (http://www.hammondmfg.com/pdf/EDB1760H.pdf).

cortina or ltp phase invertor?...solid state rectifier. Keeping the james "tone" network. The power transformer gives me 365 VDC. that would be good enough for a 5e3 i think.

I then have less watts but enough for a small gig and rehearsal amp.

could this work out?.
hobbits
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Re: geloso g1/1040 suggestions and wattage check

Postby Racing on Sat Dec 19, 2015 12:06 pm

It could certainly work out.

If you´re budget minded tho check Tubetowns housebrand of x-formers out. They´re on the last page of all their offerings. I´d wager you could muster what it takes as far as a dual EL-34 amp.

A twin 6V6 amp is normally more then loud enough though if setup right. Agreed.
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Re: geloso g1/1040 suggestions and wattage check

Postby hobbits on Sat Dec 19, 2015 4:16 pm

Hmm. Cant find that last page yout talkin about..

http://www.tube-town.net/ttstore/Transformer:::15.html housebrand. If there is a nice priced OT. I will concider going along with the el34's .
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Re: geloso g1/1040 suggestions and wattage check

Postby hobbits on Sun Dec 20, 2015 5:32 pm

thanks for the link. They also make custom face plates. Somethine to consider in the future.

I made up my mind and will go for the 6v6 tubes. With a resonal priced OT (48).

so this will be the setup;
push-pull 6v6
switchable bias between cathode and fixed
for now i stick to the ltp PI
and the james network with a FAC (like orage) controler
and the PPIMV
solid state rectifier

a nice challenge i think.

can i keep the filter caps (new one's) and the choke in the geloso setup? The 5e3 has only the 3 x 16uF caps.
hobbits
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Re: geloso g1/1040 suggestions and wattage check

Postby hobbits on Wed Dec 23, 2015 9:44 am

I found a very quick supplier...

I went for the hammond 1760H OT (for fender deluxe) and a new set of matched jj 6v6 tubes. Put it in. disconnected the fixed bias, already present in the geloso. set up the cathode bias resister and cap. fired the amp up with my "poor"man variac...no shorts and voltages seem normal. Put in the 6v6. AND. POWERRRRR. bias is very high for the 6v6 es so i have to install some bigger cathode resistors.

But i like the sound. It is nice it is clear and enough output. So my geloso problem was the OT all a long.

So for now finding the right bias resistor for the cathoide bias and then on to the switched (fixed/cathode) bias mod.

thanks for all the support.
hobbits
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Re: geloso g1/1040 suggestions and wattage check

Postby Racing on Wed Dec 23, 2015 11:28 am

Be aware that it is quite feasable to make the amp a fixed bias one too.

In such a scenario just drain the HT for voltage via a dropresistor and a diode a´la Marshall.

Edit; Oops... :mrgreen:
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Re: geloso g1/1040 suggestions and wattage check

Postby hobbits on Wed Dec 23, 2015 11:58 am

Well the geloso has the bias supply voltage on board. I'm just going to copy the fender brownface and see how it turns out.

switchable bias.. https://robrobinette.com/5e3_Modificati ... hable_Bias

and for what i think they done the same. https://www.youtube.com/watch?v=I9k-S6brvR4 (50/60 switch)
hobbits
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Re: geloso g1/1040 suggestions and wattage check

Postby Racing on Sat Dec 26, 2015 11:37 am

As food for thought.
An amp like the 1040 carries with it ample capacity to basically toss and turn to hearts desire. In this case that means that it´d be an alternative to build yourself a 4*6V6 amp down the line and thus bring the amp back to former wattage (more or less).

TBH it´s the first time i´ve ever even heard of a busted Geloso OT...but i guess there´s a first for everything.

The James network has lots of advantages and i´m sorry to say that most that fool around with guitaramps has failed to realize this. Try downloading TSC tonstack calculator if you haven´t already and bring up the James heading.
Then play around with values to hearts desire. Here´s the curveball in it all though.... :wink: . You don´t HAVE to settle for one setup. In contrast to regular "stacks" what you do is that you wire up a couple microswitches and make these engage or disengage caps..resistors and what not.
This makes for a setup wider then anything you´ve tried,guaranteed.
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