• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Best place to find replacement transformer shells

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hello everybody

I have got my hands on a geloso g221/6 amplifier with poor state and I'm in the process of rebuilding it...

The issue I face is that the transformer shells were too rusted to be replaced, and when cleaning they came to be too brittle and damaged to still have enough integrity to keep a transformer in place.

Do any of you have a hint on where to find replacement shells, either some universal kits or some geloso replacements?

I might as well call champ electronics for that as he might have spares, but he is not available those times according to his website.

Any pointers someone? This would be helpful :)

Thanks a lot!
 
Member
Joined 2015
Paid Member
I have several Geloso amplifiers on my collection and the issue you have is a common one, because they didn't do any rust prevention treatment back then. I try to avoid removing the bracing on power transformers of this type because it has been press-fitted. After the reassembly, it is almost impossible to get the original clamping pressure on the laminations to avoid mechanical buzz. They often buzz even from factory; this is one of the reasons why they changed to a different style on later amplifiers. I use a rust conversion product and then the Brasso polishing compound with good results. But if you need a full restoration, the transformer bells must be removed to inspect the insulation of the cloth wires. I attach a picture of a Geloso transformer similar to your type #5706 with bells removed: the decayed wire insulation is dangerously close to the naked end bell and to the laminations. Geloso amplifiers of this kind are still cheap and common on hamfests here; price of unrestored amplifiers is about half of what you see online, so a full restoration does make sense only if the specimen is not too far gone. Starting with a less degraded amplifier may cost less in the end. Geloso amplifier knobs are another weak point, and they are expensive to replace when missing or damaged.
 

Attachments

  • IMG_4757.jpg
    IMG_4757.jpg
    149.5 KB · Views: 221
I have the exact same except that the transformers are in a bit better shape... They had put a sheet of insulation between a part of the power transformer to avoid issues.

I plan to find either some brackets that would press hold the transformer, or replace them by other parts I have... this is for a guitar amp conversion anyway.

I think my best bet is to put a hammond power transformer I have and a toroid as OPT.

The case is half dead too, so I have put it in an electrolyte bath to rust remove the hard way, and will scrub the old paint off to put a layer of black hammerite on the whole. The shape will have to be reinforced with front and rear plates as it was bent and rusted beyond use, and the front and rear hardware was lost too.

I just hope the chokes have the same wire connection scheme as the transformers as the wires are destroyed, if this is not possible to get them back alive I'll put some active regulation.

I still keep an eye on this thread in case there is someone with spare holders, but not many hope.

Thanks anyway.
 
Member
Joined 2015
Paid Member
Guitar conversion is the best option when parts are missing and there is major corrosion. I've seen very nice results with new front and back panels and tube cage repainted on bright colors (black may not look so good). The whole purpose of rebuilding an amplifier with a peculiar vintage metalwork like this one is to have it stand out anyway.

This is the translated description of the transformers of your amplifier, according to my 1958 Geloso general catalog:

output transformer type 5706PA : for 6V6 working in class AB with 300V plate , 300V screen grid , -20V control grid. Built with two identical secundary windings, balanced relative to the primary, that may be wired for output impedences from 1.25 to 500 ohms. +/- 2dB response 75-10000Hz ; efficiency 0.86 ; max power 12W ; impedence 10K ; DC reisistence 448 ohm ; inductance 10H. There is a table with the wiring.

filter choke type 321/005 (equivalent to Z310R) : inductance 0.05H, DCR= 2 ohms, max current 300mA, suggested current 300mA

filter choke type 321/10 (equivalento to Z305R) : inductance 10H, DCR=500 ohms, max current 55mA, suggested current 45mA

power transformer type 5022: it is not yet on the 1958 catalog (the G221 amplifier was a 1960 model). The last two digits are related to the power: type 5016 is 57VA and type 5040 is 90VA. The first two digits (50) means "general use for receivers between 5 and 8 tubes".
 
Member
Joined 2015
Paid Member
I checked my Geloso spare parts bin, but I haven't found a suitable bracket. You may try to fit a modern bracket. I buy transformer parts on the enovaz.com web store, they have a wide selection of transformer end bells and brackets. Do not drill the laminations!
 

PRR

Member
Joined 2003
Paid Member
...I need the mounting channels...

End-bells need forms and a press.

Channels, any metal-knocker can bend these up. Small ones, I would ask the guy who does ducts for home heating/cooling. This is very easy work for him. Except any large channel wants a thicker gauge than his duct-metal bender can handle. But duct-guys, like audio-guys, are tool-geeks, and may have a tool or know a way.
 
I have the bells, they are in good shape

The issue for making new channels is that there is no real metal shop where I live that would be either accessible or small enough to fancy that sort of things

The best bet is to get press fit brackets that would mate and get bolted from the sides to avoid drilling
 
I just had a look at that Geloso design.
They are usually pretty good, so FR will depend very much on those OPT.

It's quite similar to my Bogens, but your 6V6 are much gentler driven.
On yours probably it will manage about 10W.

On the Bogen they are pushed right to the limit, 21-22v on the cathodes with HT of 360-370V with HT going right over 425V until the valves warm up.
 
The state of my OPT is not very good, laminations are a bit flaky and rusted...

I have made some tests on old transformers for drilling, and it came well enough that I tried it on the geloso transformers and it is finally not that bad

This is always better for me than gluing some bells with epoxy like Jan advised me by mail as I want to be able to dismantle them easily... added benefit to get a better press on the laminations which are not very stable

I have to salute the great service of Jan from ASK JAN FIRST who was very friendly and willing to help!
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.