Hacker Mayflower II (RV20) enquiry. - UK Vintage Radio Repair and Restoration Discussion Forum

Nanozeugma · 18th Feb 2019, 4:30 pm

Hi all,
I'm in the early stages of refurbishing a Hacker RV20.
It appears to have had *some* work done as the main reservoir / smoothing can is just a shell with two modern electrolytics jammed inside.
Little else, however, appears to have been done to it.
It works - but it suffers from low frequency oscillation (motor boating).

Just looking at the components, I arrived at R2 which feeds the screen grid of V2 on pin 8 (an EF89) - and appears to have been sweating quite a bit.

The schematic suggests this should be 47K, it reads 77k and the colour code (although difficult to determine due to the effects of heat) doesn't look like it was ever 47k.

I wondered if any kind soul in possession of an RV20 would be kind enough to confirm the value of R2 fitted to theirs?

N.B. I am *not* suggesting this is causing the motor boating.

T.I.A.

TowerRadio · 18th Feb 2019, 6:38 pm

The component list shows R2 as 4.7K. Which one is right? I can't get to my model at the moment, it's on a to do list and tucked away somewhere (it works brilliantly though the bridge rectifier needs replacing) Les

ronbryan · 18th Feb 2019, 7:05 pm

The Mayflower 1 (RV14) uses the same circuit for V2 as the Mayflower II and that has a 47k screen grid resistor R2 specified in the schematic and the parts list and that is confirmed from an under-chassis photo of an RV14 that I repaired.

A value of 4k7 would be highly unlikely as a screen grid resistor for an IF valve and surely must be a misprint in the RV20 parts list.

Ron

Nanozeugma · 18th Feb 2019, 8:19 pm

Ron: Thanks for the confirmation - and - as suspected 4k7 appears as a misprint.
Les: Thanks for your input.

Colin.

18th Feb 2019, 4:30 pm	#1
Nanozeugma Heptode Join Date: Nov 2017 Location: London, UK. Bury, Lancashire quite regularly :) Posts: 611	Hacker Mayflower II (RV20) enquiry. Hi all, I'm in the early stages of refurbishing a Hacker RV20. It appears to have had some work done as the main reservoir / smoothing can is just a shell with two modern electrolytics jammed inside. Little else, however, appears to have been done to it. It works - but it suffers from low frequency oscillation (motor boating). Just looking at the components, I arrived at R2 which feeds the screen grid of V2 on pin 8 (an EF89) - and appears to have been sweating quite a bit. The schematic suggests this should be 47K, it reads 77k and the colour code (although difficult to determine due to the effects of heat) doesn't look like it was ever 47k. I wondered if any kind soul in possession of an RV20 would be kind enough to confirm the value of R2 fitted to theirs? N.B. I am not suggesting this is causing the motor boating. T.I.A. __________________ Thermionic Emission, warms the cockles of your tubes.

18th Feb 2019, 6:38 pm	#2
TowerRadio Hexode Join Date: Mar 2008 Location: Bristol, UK. Posts: 388	Re: Hacker Mayflower II (RV20) enquiry. The component list shows R2 as 4.7K. Which one is right? I can't get to my model at the moment, it's on a to do list and tucked away somewhere (it works brilliantly though the bridge rectifier needs replacing) Les

18th Feb 2019, 7:05 pm	#3
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Hacker Mayflower II (RV20) enquiry. The Mayflower 1 (RV14) uses the same circuit for V2 as the Mayflower II and that has a 47k screen grid resistor R2 specified in the schematic and the parts list and that is confirmed from an under-chassis photo of an RV14 that I repaired. A value of 4k7 would be highly unlikely as a screen grid resistor for an IF valve and surely must be a misprint in the RV20 parts list. Ron

18th Feb 2019, 8:19 pm	#4
Nanozeugma Heptode Join Date: Nov 2017 Location: London, UK. Bury, Lancashire quite regularly :) Posts: 611	Re: Hacker Mayflower II (RV20) enquiry. Ron: Thanks for the confirmation - and - as suspected 4k7 appears as a misprint. Les: Thanks for your input. Colin. Attached Thumbnails __________________ Thermionic Emission, warms the cockles of your tubes.