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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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Thread Tools |
2nd Jun 2019, 10:19 am | #1 |
Pentode
Join Date: Oct 2018
Location: Coventry, West Midlands, UK.
Posts: 220
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Bush VHF 61 Tuning Indicator
I have just finished restoring a Bush VHF 61 but have a minor irritation with the tuning indicator. On VHF the indicator works well showing full deflection when a strong station is tuned but on MW or LW the indicator barely moves at all. The station is coming through strongly and there is little or no difference in output volume between VHF, MW & LW, just the tuning indicator doesn't seem to work well on MW or LW. Checking the grid voltage on the tuning indicator shows around -7 to -8v when a VHF station is tuned but only around -0.8v when a MW or LW station is tuned.
All the Hunts caps in the set have been replaced and all voltages on the valves are in spec so not really sure where to look next. Any suggestions appreciated! |
2nd Jun 2019, 10:33 am | #2 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Bush VHF 61 Tuning Indicator
Trader sheet refs, check S18 contacts and the AGC feed resistor R22, if they're ok measure the AGC voltage at the junction of R21 and R22 when a strong AM station is tuned in.
Lawrence. |
2nd Jun 2019, 10:40 am | #3 |
Pentode
Join Date: Oct 2018
Location: Coventry, West Midlands, UK.
Posts: 220
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Re: Bush VHF 61 Tuning Indicator
Thanks, I did look at the switch contacts and they seemed good but will check again and check the resistors.
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2nd Jun 2019, 2:52 pm | #4 |
Pentode
Join Date: Oct 2018
Location: Coventry, West Midlands, UK.
Posts: 220
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Re: Bush VHF 61 Tuning Indicator
Checked the switch contacts and all OK, R21 & R22 were in spec but swapped them out just to be sure. With a strong MW station I'm getting around -1.5v at junction of R21/R22 which gives around -1.4v at the grid of the indicator and only a small deflection so no luck so far I'm afraid.
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2nd Jun 2019, 3:02 pm | #5 |
Octode
Join Date: Jan 2003
Location: Guildford, Surrey, UK.
Posts: 1,960
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Re: Bush VHF 61 Tuning Indicator
I dimly recollect that this set's slider wavechange switch has HT+ wired to a contact adjacent to the AGC line contact. Leakage or tracking across the paxolin insulation can cause the AGC line to be biased more in the positive direction, thus limiting the eye deflection on AM.
Ron |
2nd Jun 2019, 3:55 pm | #6 |
Dekatron
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 5,000
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Re: Bush VHF 61 Tuning Indicator
There isn't any fault with your radio, this is just how they are on AM.
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2nd Jun 2019, 6:01 pm | #7 | |
Pentode
Join Date: Oct 2018
Location: Coventry, West Midlands, UK.
Posts: 220
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Re: Bush VHF 61 Tuning Indicator
Quote:
@Techman Thanks, I had read that AM reception was not brilliant on these but there was definitely something not quite right as there was hardly any movement at all on the indicator. Thanks everyone for the help. |
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