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G8BBZ · 7th Dec 2022, 4:44 pm

Hi Erik,
On closer inspection I realise that the RF Amp in the MCU6 is more similar to that in the R551 than the amp in the R499. The R499 amp has two balanced stages of amplification versus one in the R551 and MCU6.
I attach the circuit of the R551 front end in case you don't have it available.
The 100mA fuse in the MCU6 has been changed to a 250mA in the R551 but located on the primary side of the transformer. There is a 30MHz LPF on the output of the R551 amp to stop any stray 38MHz getting through to the first IF.
Apart from that I think the amplifiers are very similar.
Hope this helps

7th Dec 2022, 4:44 pm	#8
G8BBZ Pentode Join Date: Oct 2005 Location: Hebden Bridge, West Yorkshire, UK. Posts: 200	Re: Redifon MCU6B Hi Erik, On closer inspection I realise that the RF Amp in the MCU6 is more similar to that in the R551 than the amp in the R499. The R499 amp has two balanced stages of amplification versus one in the R551 and MCU6. I attach the circuit of the R551 front end in case you don't have it available. The 100mA fuse in the MCU6 has been changed to a 250mA in the R551 but located on the primary side of the transformer. There is a 30MHz LPF on the output of the R551 amp to stop any stray 38MHz getting through to the first IF. Apart from that I think the amplifiers are very similar. Hope this helps Attached Thumbnails __________________ Peter G8BBZ