• 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.

Geloso G3272A

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#2
It is not important , if in that chart there are the usual impedances like 4 , 8 ohm .
The output transformer is made with 2 independent secondaries each with 4 wires in total - the 2 x 4 screws on the back that need to be wired right for your speakers .
 
#3

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#7
According to the official Geloso documentation, the connections marked with "balanced line" are the only ones to use when the speaker cables are very long, also the terminals marked with the square must be connected to the chassis: you can use the screw under the speaker terminals . Geloso amplifiers of this type were often installed on churches. Search for "Bollettino tecnico geloso 99a" (1966) to get the product sheet with the diagram. According to the product description, this 75W amplifier is the best choice for public places that can accommodate up to 1000 people, or can be used to drive up to 50 ceiling speakers. The Geloso main filter capacitors were built in-house and do not age well. Be sure to check if they have already been replaced before turning on the amplifier. The original "death capacitors" on the transformer primary side are almost always leaky and must be disconnected.
 
#9
The G3272A is the fourth revision of a design started in 1949 with the G275A (also sold as kit); the chassis was "modernized" and rebranded G260A, then G272A and finally G3272A. The G3272A is the only one specified for full audio bandwith, with a improved output transformer.
 
#10
I bought it for the 807 tubes because I have 2 pairs of each for an endless DIY amplifier project that never finished. Hope some day I will do. I saw in Electronic Tube Handbook that 807 has the lowest THD so I bought 4 tubes but never finished.
Thanks for all the replies and information.
 
#12
invacuo said:
I saw in Electronic Tube Handbook that 807 has the lowest THD so I bought 4 tubes but never finished.
Click to expand...
As the 807 (Philips designation QE06/50) is a member of the vast 6L6 family, your findings will apply to all family members as well.

Basically, the 807 is a 6L6G with slightly increased plate dissipation ratings, UX-5 base instead of I.O., internal shieldings and it's plate connection brought out with a top cap, which not only separates the grid and plate circuitries in RF applications, but also enables this tube to cope with higher plate voltages.

Best regards!
 
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