Marconi TF801A now working. - UK Vintage Radio Repair and Restoration Discussion Forum

M0XNA Neil · 6th Sep 2015, 6:43 pm

I have just finished and tested the TF801A RF signal generator and it is oscillating (CW & MCW) on all ranges from 8MHz to 260MHz. I have not only changed all the electrolytics, but replaced the EC53 triode, but also replaced the two EA50 diodes with Silicon BAW62 signal diodes. I am getting 330mV P-P wirh 0dB on the attenuator on the 8 to 19 MHz range.

The inside of this instrument is a work of art! Here are some photographs.

Neil

Phil G4SPZ · 6th Sep 2015, 11:12 pm

Well done! It's nice to see some of this classic and very high quality test gear restored to working order.

M0XNA Neil · 7th Sep 2015, 7:25 am

I am amazed at how stable the frequency is when set. The fine tuning offset control lets you set a very precise frequency. Also, given the quality of this instrument, the attenuators are incredible quality. I shall use this on my next valve comms receiver build!

Neil

m0cemdave · 7th Sep 2015, 10:56 am

Congratulations on an excellent job, and for giving it a good home.

lesmw0sec · 7th Sep 2015, 10:59 am

If it is the one I recall, it is a very nice piece of kit. The one I had was lacking an oscillator valve and being unable to get a replacement, I used a FET instead. The carrier strength was a bit up & down over the range, but it did the job.
Interesting to see the Advance genny in the back. I also have one of those, not that it gets much use since I built a DDS unit.

M0XNA Neil · 7th Sep 2015, 11:17 pm

Dave,
Thanks for the generator, I ended up changing all the electrolytics for modern capacitance equivalents. All the large valves worked fine. I decided to slot the Silicon diodes into the EA50 valve holders and they also worled fine.

M0XNA Neil · 7th Sep 2015, 11:20 pm

Les,

I purchased an EC53 from ebay for about £6. I thought about the FET option, but the RF level pot can apply around 200V onto the EC53's anode for some bands.

I also have an Advance P1 genny which also works well.

6th Sep 2015, 6:43 pm	#1
M0XNA Neil Tetrode Join Date: Apr 2009 Location: Towcester, Northamptonshire, UK. Posts: 92	Marconi TF801A now working. I have just finished and tested the TF801A RF signal generator and it is oscillating (CW & MCW) on all ranges from 8MHz to 260MHz. I have not only changed all the electrolytics, but replaced the EC53 triode, but also replaced the two EA50 diodes with Silicon BAW62 signal diodes. I am getting 330mV P-P wirh 0dB on the attenuator on the 8 to 19 MHz range. The inside of this instrument is a work of art! Here are some photographs. Neil Attached Thumbnails __________________ An engineer makes for a penny what a scientist makes for a pound!

6th Sep 2015, 11:12 pm	#2
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: Marconi TF801A now working. Well done! It's nice to see some of this classic and very high quality test gear restored to working order. __________________ Phil Optimist [n]: One who is not in possession of the full facts

7th Sep 2015, 7:25 am	#3
M0XNA Neil Tetrode Join Date: Apr 2009 Location: Towcester, Northamptonshire, UK. Posts: 92	Re: Marconi TF801A now working. I am amazed at how stable the frequency is when set. The fine tuning offset control lets you set a very precise frequency. Also, given the quality of this instrument, the attenuators are incredible quality. I shall use this on my next valve comms receiver build! Neil __________________ An engineer makes for a penny what a scientist makes for a pound!

7th Sep 2015, 10:56 am	#4
m0cemdave Octode Join Date: Feb 2009 Location: Bletchley, Buckinghamshire, UK. Posts: 1,219	Re: Marconi TF801A now working. Congratulations on an excellent job, and for giving it a good home.

7th Sep 2015, 10:59 am	#5
lesmw0sec Octode Join Date: Jul 2009 Location: Carmel, Llannerchymedd, Anglesey, UK. Posts: 1,506	Re: Marconi TF801A now working. If it is the one I recall, it is a very nice piece of kit. The one I had was lacking an oscillator valve and being unable to get a replacement, I used a FET instead. The carrier strength was a bit up & down over the range, but it did the job. Interesting to see the Advance genny in the back. I also have one of those, not that it gets much use since I built a DDS unit.

7th Sep 2015, 11:17 pm	#6
M0XNA Neil Tetrode Join Date: Apr 2009 Location: Towcester, Northamptonshire, UK. Posts: 92	Re: Marconi TF801A now working. Dave, Thanks for the generator, I ended up changing all the electrolytics for modern capacitance equivalents. All the large valves worked fine. I decided to slot the Silicon diodes into the EA50 valve holders and they also worled fine. __________________ An engineer makes for a penny what a scientist makes for a pound!

7th Sep 2015, 11:20 pm	#7
M0XNA Neil Tetrode Join Date: Apr 2009 Location: Towcester, Northamptonshire, UK. Posts: 92	Re: Marconi TF801A now working. Les, I purchased an EC53 from ebay for about £6. I thought about the FET option, but the RF level pot can apply around 200V onto the EC53's anode for some bands. I also have an Advance P1 genny which also works well. __________________ An engineer makes for a penny what a scientist makes for a pound!