Help required please, Marconi TF 1370A - UK Vintage Radio Repair and Restoration Discussion Forum

billy.bates · 2nd Mar 2021, 8:25 pm

Hi, I have been repairing a Marconi TF 1370A wide band signal generator & I'm trying to get it to its original spec on the 400Hz & 1KHz frequencies which should be within 0.5%. Currently I'm at 0.6 & 0.8%, I have gone through replacing out of tolerance carbon comp' resistors, the HT & LT supplies are spot on & most of the caps have been replaced or are good. Any ideas/help would be most welcome! God bless, Bill.

WME_bill · 3rd Mar 2021, 6:13 pm

Marconi TF1370. AF Oscillator.
Wein bridge oscillator, with variable capacitor for tuning and switched resistors for each range. There are trimmer resistors and also a little trimmer capacitor for the top end of each range. Surely you just need to tweek those. Ranges B and C. Lovely smooth tuning with the variable capacitor.
When tweaking, you will have to be prepared to put the screening covers back on for the higher frequency ranges.
The frequency accuracy quoted in the manual and 1972 catalogue is 2%, so I think you have done well to improve it so much.
wme_bill

billy.bates · 12th Mar 2021, 1:52 pm

Thanks for your response, I'll investigate & see where I get to. Thanks!
God bless, Bill.

2nd Mar 2021, 8:25 pm	#1
billy.bates Triode Join Date: Dec 2017 Location: Chester, Cheshire, UK. Posts: 13	Help required please, Marconi TF 1370A Hi, I have been repairing a Marconi TF 1370A wide band signal generator & I'm trying to get it to its original spec on the 400Hz & 1KHz frequencies which should be within 0.5%. Currently I'm at 0.6 & 0.8%, I have gone through replacing out of tolerance carbon comp' resistors, the HT & LT supplies are spot on & most of the caps have been replaced or are good. Any ideas/help would be most welcome! God bless, Bill.

3rd Mar 2021, 6:13 pm	#2
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Help required please, Marconi TF 1370A Marconi TF1370. AF Oscillator. Wein bridge oscillator, with variable capacitor for tuning and switched resistors for each range. There are trimmer resistors and also a little trimmer capacitor for the top end of each range. Surely you just need to tweek those. Ranges B and C. Lovely smooth tuning with the variable capacitor. When tweaking, you will have to be prepared to put the screening covers back on for the higher frequency ranges. The frequency accuracy quoted in the manual and 1972 catalogue is 2%, so I think you have done well to improve it so much. wme_bill Last edited by WME_bill; 3rd Mar 2021 at 6:25 pm.

12th Mar 2021, 1:52 pm	#3
billy.bates Triode Join Date: Dec 2017 Location: Chester, Cheshire, UK. Posts: 13	Re: Help required please, Marconi TF 1370A Thanks for your response, I'll investigate & see where I get to. Thanks! God bless, Bill.