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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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25th May 2020, 12:07 pm | #1 |
Tetrode
Join Date: Apr 2015
Location: Chester, Cheshire, UK.
Posts: 62
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Dynatron Tourist TP14 problem
Hi everyone.
This bank holiday I’ve decided to try and resurrect an old Dynatron Tourist. The set is essentially dead, apart from a pop from the speaker when switched on, I’ve replaced the capacitors to no avail but when I probed the transistor voltages they are way off the values given in the service sheet. The voltages are (in the order of Emitter, Collector, Base respectively): VT1: 0.5, 4.3, 0.6 VT2: 0.3, 4.1, 0.4 VT3: 0.5, 4.0, 0.7 VT4: 0.7, 4.7, 0.8 VT5: 1.3, 1.8, 1.3 VT6: 1.3, 4.7, 0.7 I’ve checked the battery and it’s a little over 9V so the supply is fine - can anyone suggest any reasons for the low voltages? Thanks Paul |
25th May 2020, 1:04 pm | #2 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,289
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Re: Dynatron Tourist problem
Given that VT5 and VT6 collectors are connected to the negative rail via the output transformer primary winding something would appear to be seriously wrong. Only about 0.1V should be dropped in the windings.
Are you measuring voltages wrt the positive rail?
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
25th May 2020, 1:38 pm | #3 |
Tetrode
Join Date: Apr 2015
Location: Chester, Cheshire, UK.
Posts: 62
|
Re: Dynatron Tourist TP14 problem
Graham,
Thanks for your reply - I’ve just diagnosed the problem: One of the output transistors was reading as a depletion mode N-channel MOSFET so was obviously causing a catastrophic problem with the circuit. I’ve fitted another OC78 and the set is working! Thanks again Paul |
25th May 2020, 1:51 pm | #4 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,289
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Re: Dynatron Tourist TP14 problem
Wow! Only three posts to fix the fault. That must be a record.
__________________
Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |