31-07-2020, 10:48 PM
(This post was last modified: 31-07-2020, 10:50 PM by Mike Watterson.)
I couldn't resist looking at the PSU.
At the 230 to 250V setting the DK91/1R5 (the last valve in the chain) had just about a volt. So no reception.
At the next setting it had 1.26 but dropping. The HT is a healthy and steady 87V at the 210 to 225 setting. Should be about 84V on the 250V tap with 240V AC. The intermediate DC taps are actually also AC intermediate voltages.
The HT to LT dropper is supposed to give about 6.5 to 7.0V. It was 5.6V. The 1800 Ohms measured 1970 Ohms. I replaced that with 1k in series with 750 Ohms. The LT was briefly 1.37V but dropped to 1.28.
The 750 R is a vintage resistor, it may be going high.
I also suspect the 100uF capacitor that's decoupling the last 3 of the five filaments. It's one of those 2 part plastic cased electrolytics that are often faulty. The main HT caps seem OK as the HT is stable 87V.
Some reception at the HF end of MW, still no R5 and I think a short on one of the tuning gangs just after the half way closed point. Arrgh.
Definitely no more tonight. Reading time. Patricia Wentworth, "The Silent Pool" tonight. Miss Maud Silver would give Miss Marple or Jessica Fletcher a run!
At the 230 to 250V setting the DK91/1R5 (the last valve in the chain) had just about a volt. So no reception.
At the next setting it had 1.26 but dropping. The HT is a healthy and steady 87V at the 210 to 225 setting. Should be about 84V on the 250V tap with 240V AC. The intermediate DC taps are actually also AC intermediate voltages.
The HT to LT dropper is supposed to give about 6.5 to 7.0V. It was 5.6V. The 1800 Ohms measured 1970 Ohms. I replaced that with 1k in series with 750 Ohms. The LT was briefly 1.37V but dropped to 1.28.
The 750 R is a vintage resistor, it may be going high.
I also suspect the 100uF capacitor that's decoupling the last 3 of the five filaments. It's one of those 2 part plastic cased electrolytics that are often faulty. The main HT caps seem OK as the HT is stable 87V.
Some reception at the HF end of MW, still no R5 and I think a short on one of the tuning gangs just after the half way closed point. Arrgh.
Definitely no more tonight. Reading time. Patricia Wentworth, "The Silent Pool" tonight. Miss Maud Silver would give Miss Marple or Jessica Fletcher a run!
