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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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16th Jan 2023, 9:14 am | #1 |
Triode
Join Date: Oct 2017
Location: Madrid, Spain.
Posts: 39
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Rock-ola Capri 100, amplifier.
Hello Everyone.
I open this post discussion because I found the sound totally lack of TREBLE, and poor of BASS, only middle frequencies seems to sound good. What do you think about the capacitors replacement at amplifier, the Juke box has been more than 30 years without turning on.? I have read the better thing to do is changing all capacitors, others think only some of them? what are more common type due to fault? I have thought to measure with multimeter all capacitors and change only the fault ones... What do you suggest please? |
16th Jan 2023, 9:20 am | #2 |
Heptode
Join Date: Oct 2019
Location: Täby, Sweden
Posts: 704
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Re: rockola capri 100, amplifier
I think a circuit diagram and/or pictures helps. Then the circuit can be assessed for the issue, and the pictures can be reviewed for general condition of the apparatus.
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16th Jan 2023, 9:25 am | #3 |
Triode
Join Date: Oct 2017
Location: Madrid, Spain.
Posts: 39
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Re: rockola capri 100, amplifier
thank you Richard for your quick reply.
I have attached the diagram, but not the amplifier, because is not disassembled yet, Ill do it ASAP. Carlos |
16th Jan 2023, 9:54 am | #4 |
Triode
Join Date: Oct 2017
Location: Madrid, Spain.
Posts: 39
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Re: Rock-ola Capri 100, amplifier.
I have attached two amplifier pics...
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16th Jan 2023, 10:01 am | #5 |
Banned
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Re: Rock-ola Capri 100, amplifier.
I can see a couple of VERY pregnant electrolytic caps there. I cant see values or labels.
There are also a lot of "Dart " branded capacitors, I have never seen them before but they look like paper capacitors. These should be checked on a decent ESR meter that measures at the actual voltage in the circuit. ALL the resistors I see can be very drifting in value. Mostly they get higher in value as they are carbon composition resistors. Very low values will probably pass a test, but anything over about 22k or 47k will be very suspect. Apart from value shift, they can also be very noisy!!. Joe |
16th Jan 2023, 10:34 am | #6 |
Triode
Join Date: Oct 2017
Location: Madrid, Spain.
Posts: 39
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Re: Rock-ola Capri 100, amplifier.
Thank you Joe; I would,nt like to change randomly the caps...
but I got inform electrolytic caps should be recommended to change after twenty years even so, if the machine has been without connecting... due to these caps get dry quite often... Close to the tones knobs there are four 0,1 caps value... these look like not very good, with a CAP MULTIMETER this kind of values are difficult to test because of a fluctuating measure... do you suggest to change almost all the electrolytic caps? |
16th Jan 2023, 11:17 am | #7 |
Dekatron
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Location: Seaford, East Sussex, UK.
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Re: Rock-ola Capri 100, amplifier.
Before you continue to use the amplifier you need to replace the audio coupling capacitors that connect the phase splitter to the output stage grids. Faults in the output stages can cause expensive damage to the transformers and valves.
Old paper capacitors fail by electrical leakage and this affects the DC operating conditions of the valves. Simple capacitor testers do not measure leakage which must be measured at the working voltage of the capacitor. If you post the picture of the full amplifier we can advise you on the parts to replace. |
16th Jan 2023, 11:32 am | #8 |
Dekatron
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Location: Chesterfield, Derbyshire, UK.
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Re: Rock-ola Capri 100, amplifier.
Hi Carlos can you give us the voltage readings on the output valves there are four 6973's, be careful you should have around 350/370 on two of the pins, 8 and9 and a negative voltage around 25 volts on pin six.as Joe said the electrolytics may well need replacing especially the 200uf smoothing , Mick.
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16th Jan 2023, 11:45 am | #9 |
Triode
Join Date: Oct 2017
Location: Madrid, Spain.
Posts: 39
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Re: Rock-ola Capri 100, amplifier.
Thank you everyone, i dont want to take any step without making sure what I,m doing... appreciate your help.
The thing is; there are two top treble speakers which only makes hum. and bass sound is quite poor... only middle frequencies seems to work ok... |
16th Jan 2023, 6:25 pm | #10 |
Triode
Join Date: Oct 2017
Location: Madrid, Spain.
Posts: 39
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Re: Rock-ola Capri 100, amplifier.
I, m think I,m going to wait up to I get more information.
I dont want to changes capacitor without test them, my multimeter has a basic scale and consider it is not very reliable. |
16th Jan 2023, 7:00 pm | #11 |
Moderator
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Re: Rock-ola Capri 100, amplifier.
To test the paper capacitors, you need a high voltage leakage tester. Ordinary multimeters won't show anything wrong with a part that would destroy your output valves and transformers.
To test electrolytic capacitors, you need to do leakage at the appropriate voltage, and ideally also check the equivalent SERIES resistance (ESR). For the DC blocking capacitors from phase shifter stages to the grids of the output valves, you might just as well replace them. These are the ones which can do real damage. David
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16th Jan 2023, 7:30 pm | #12 |
Triode
Join Date: Oct 2017
Location: Madrid, Spain.
Posts: 39
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Re: Rock-ola Capri 100, amplifier.
Thank you Dave
""""""""""For the DC blocking capacitors from phase shifter stages to the grids of the output valves, you might just as well replace them. These are the ones which can do real damage"""""" do you refer to the marks with white arrows; please? Sorry for my knownledge, its the first time I open a valve amplifier... Thats why I want to make sure every step I take Regards. |
16th Jan 2023, 8:17 pm | #13 |
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Re: Rock-ola Capri 100, amplifier.
I don't know the specific amplifier so I can't say from the picture. Assuming the amp has a push pull output stage, find the output valves. There will be four of them. `then look up the data for their type and find which pin connects to grid number 1. Trace connections to each of these and look for a capacitor of about 0.1 microfarads. These will be the ones
David
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16th Jan 2023, 8:33 pm | #14 |
Dekatron
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Location: Chesterfield, Derbyshire, UK.
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Re: Rock-ola Capri 100, amplifier.
This amplifier uses 6973's x4 with fixed bias I have never had to replace the coupling capacitors the brown ones like in this amp ,the 25volt neg is derived from the power supply I allways replace the neg smoothing capacitor. and the two 200uf in the HT doubler cct. Mick.
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16th Jan 2023, 8:55 pm | #15 |
Hexode
Join Date: Dec 2019
Location: Hohenroda, Eastern Hesse, Germany
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Re: Rock-ola Capri 100, amplifier.
I've got a 1967 Rock Ola 434 Concerto in my dining room. Due to rather frequent usage it has eaten up rather fast the 6CY7 drivers twice, and finally all electrolytics were beyond trustworthiness. Yes, some resistors can go high value but mine have not yet.
Check all pots thoroughly: If the machine has spent it's first life in a smoker's pub the pots can have become from cracklin' to o/c. In healthy condition those machines give a full and warm sound (such as the power consumption does suggest!). Joe |
16th Jan 2023, 11:00 pm | #16 | |
Dekatron
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Re: Rock-ola Capri 100, amplifier.
Quote:
As well as the AC mains voltage and AC voltages from mains transformer, there will be numerous DC voltages at components and valve electrodes, these DC voltages can be well in excess of 200 volts, maybe as high as 300V, these voltages can seriously bite ! Edit Update - 350/370V from Post 8. David Last edited by DMcMahon; 16th Jan 2023 at 11:08 pm. Reason: Update |
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17th Jan 2023, 2:37 am | #17 |
Triode
Join Date: Oct 2017
Location: Madrid, Spain.
Posts: 39
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Re: Rock-ola Capri 100, amplifier.
Thank you Everyone for the help offered!!
David the safe is the main thing to take care about due the high voltage at main power and amplifier comes, thanks a lot for your info and very useful advice. I can say the jukebox sound is not bad, but should be better than it is due the kind of machine it is... So maybe the reason for that, is a couple of components that should be worn out, or maybe an easiest thing... When started, changed the Astatic cartridge for another ceramic one... but I did not get any sound improvement... I,m going to do a spotlight cleaning of pots as Joe_lorenz has explain, because the machine has surely been in a pub at first time. Always point at capacitors according what I have read about filters and frequencies, That is why I asked what are they the more common due to fault, In all recommendations for changing them, exist different opinions. Thanks a lot, i will keep inform. Regards |
17th Jan 2023, 5:58 pm | #18 |
Triode
Join Date: Oct 2017
Location: Madrid, Spain.
Posts: 39
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Re: Rock-ola Capri 100, amplifier.
Hello Everyone!
Two points; 1. The treble sound issue has been solved. I opened the top speakers and there is a quite hide pot to set up these speakers... Sorry about that, but thats was the problem, i,m not acquainted in these kind of machine. 2. It probably has to sound with a deeper bass, but I,m not going to "touch" the amplifier anymore it probably is working at 80%... now, my opinion at this point is better no operate the amp. Some filter, some cap, some resistor... are not working at 100%, but the sound quality is not bad. I do not owned a proper cap multimeter, so I think is better to enjoy the rest of restoration and maybe in the future, it the sound quality turns bad, I will sort out... I think so... I would say thank you to everyone who has replay and interested in this issue, and hope it helps also. Regards. |
17th Jan 2023, 10:25 pm | #19 | |
Dekatron
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Re: Rock-ola Capri 100, amplifier.
Quote:
This is normal and there normally will be valid reasons for the various recommendations given. I admit depending upon one's experience it can be confusing at times. David |
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18th Jan 2023, 1:50 pm | #20 | |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,603
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Re: Rock-ola Capri 100, amplifier.
Quote:
Carlos I understand your reasoning above but I would advise you still consider the advice given in Post # 7 which advised replacing the coupling capacitors from the phase splitters to the output valves grids because as stated, if the capacitors are bad (high leakage) then worst case is that the output valves and/or the output transformers could become damaged. For the Forum to advise which capacitors these are, the full amplifier schematic or a section showing the output valves should be posted. You could measure (bear in mind your personal safety) the control grids of the output valves to make sure there is no +ve DC voltage present, but even if there is no +ve voltage, it may still be best to replace the coupling capacitors for future long term reliability. David |
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