616
Item nr.

Mayfair 355 AC/DC set

The Design

A few details of the schema. ONE: The 35W4 rectifier has a split heater. Many radio's use one section as parallel shunt to the dial light, so that the light will not die from the startup surge of the cold filaments. But here, one section of the heater is used as a limiter for the rectifier and prevents high startup currents through the buffel elco. TWO: The converter is not of the common pentagrid type, but instead a penthode 12AU6 is used. I think this may degrade performance, so why? The screen grid is not on constant voltage but has negative feedback from the IF transformer. THREE: There is no IF stage! So, with just little amplification this set sn't very sensitive, and there is only one IF transformer so selectivity is also near the bottom. FOUR: Two resistors and two capacitors between the AF preamp and output are combined into a single integrated unit with four wires. FIVE: There is no Automated Gain Control (AGC). SIX: The radio has a "floating chassis", where the circuitry is not directly connected to the metal base of the construction, but only through a 50n capacitor.

The external design is simple but efficient. While in Europe, dark and even black designs are the rule and colorful designs the exception, in the USA I see a lot of colorful radio's and just incidentally a black radio. The big dial knob is mounted directly onto the condensor axis, and if you pull it, you can touch the inside of the radio rightaway, BUT YOU SHOULDN'T! The dial is marked in multiples of 10kc (which is usual for American radio's) and has no Conelrad marks, because these were not invented yeat in 1952.

I guess the radio was made around 1952 because the tubes carry codes like 52. I estimate the power consumption to be around 23W, I can't directly measure powers at 110V.

This Object

First, I never get used to these elco's just dangling around under the chassis. I didn't trust the old elco can, so first replaced it by a can from my stock. When the crackling appeared, I replaced it by another can but with no avail. But when all was fixed and I tried to put back the chassis, it didn't fit because my can was too thick and I replaced the elco's for the third time.

I replace old paper caps and elco's routinely so started by replacing seven caps. Then, on firing the radio up, all I heard was the infamous crackling. I cleaned all tube pins and holders with ammonia but that didn't help any. Neither did replacing the elco again. I swapped the rectifier 35W4 with the one in my Teletone 11, which cleared the rectifier of suspicion. I replaced the R-C network between tubes 2 and 3, also with no effect. I thought maybe there was something wrong with the converter or detector tubes, so oredered 12AV6 and 12AY6 tubes, placed them, but no effect. I took out the volume pot, opened it, gave it a good clean an placed it back, but no improvement. I took out the IF can and opened it, and found there was some dark dusty stuff inside. Removed some with a screw driver, built back the IF can, and found the problem gone!

What followed was a short episode in my repair carreer that I'm not very proud of. I found the crackling gone, but still no station was heard; actually, in my area I receive on AM radio's just one station, namely Radio Paradijs. But not on the Mayfair! Disappointed, I left the project alone for a few days, until I saw the light... Many radio's, with a ferrite rod mounted along the long side of the radio, receive stations in the front and back, but are deaf to the left and right. But this Mayfair has a loop antenna in the back, which means it is deaf to the front and back direction. After I realised this, I rotated the radio by 90 degrees and heard Radio Paradijs come through!