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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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31st Jul 2019, 9:34 am | #1 |
Triode
Join Date: Nov 2018
Location: Swindon, Wiltshire, UK.
Posts: 43
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Hacker Sovereign II RP25A
Hi All,
I have managed to get this radio working. The fault was traced to T4 AC128 in the output stage. T3 was found to be working correctly.The transistor was tested on my Atlas Semiconductor Tester. The result: Faulty device. I have however another problem. The ouptut is distorted on all wavebands and the pointer is not in agreement on any waveband. I did change T1 and T2 on the output stage board to BC548 Transistors. The volume level is not particularly high on any waveband. I did buy this radio from EBay, so I do not know for certain if any of the presets have been altered which would upset the performance of the set. I would be grateful for any help please. Thank you. |
31st Jul 2019, 3:20 pm | #2 |
Triode
Join Date: Nov 2018
Location: Swindon, Wiltshire, UK.
Posts: 43
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Re: Hacker Sovereign II RP25A
Further to my message, the radio in question has now decided to pack up altogether. There is a hiss in the speaker but no RF. I have had the IF(AM) board out today to try and find the cause of the distortion without any luck. I cannot now inject a signal into the switchboard form the collector of T1 on that board. A signal can be injected into the amplifier which is absolutely fine.
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31st Jul 2019, 4:14 pm | #3 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
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Re: Hacker Sovereign II RP25A
Replacing the BC148s with BC548s will be straightforward. Presumably you have replaced the AC128. You will need to adjust the quiescent current as per the service instructions.
It sounds as if you have a fault in the IF stages, possibly a BC194/5 which are prone to failure, but check you haven't disturbed something. |
31st Jul 2019, 10:57 pm | #4 | |
Triode
Join Date: Nov 2018
Location: Swindon, Wiltshire, UK.
Posts: 43
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Re: Hacker Sovereign II RP25A
Quote:
The T4 transistor on the audio board I replaced with an AC188. I do not have any good AC128 examples in stock. Sorting through these I found several I had in stock were completely faulty and had to be discarded. There are plenty around on EBay but the average price is now about £3.95 each. It is not possible to order any at the moment. I am sorry to perhaps ask a trivial question, but is the RV4 preset the control that will need adjusting by removing the link connected to T5? I will try and find the problem with the IF(AM) board first. It may be possible that I have disturbed something when doing component tests. |
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31st Jul 2019, 11:33 pm | #5 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,786
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Re: Hacker Sovereign II RP25A
I don't know the quiescent adjustment procedure as I don't have the service info to hand, but with sets of this era the procedure normally involves removing a solder link and measuring the current or voltage across it while adjusting a preset. You don't need to worry about this at this stage unless the adjustment is hugely out as you will just get low volume distortion or a bit of excess current.
Lots of these Ge small signal output transistors are developing internal shorts now, just like the AF11xs a decade ago. The only permanent solution is to convert the radio to silicon, which isn't too d|ifficult but not somewhere you should be going to at this stage. See https://www.vintage-radio.net/forum/...ad.php?t=54342 |