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VanArn

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About VanArn

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  • Birthday 25/07/1941

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  1. I am not familiar with the Univector arm and like Tweaky indicates, it does not look as if it has suffered any major physical damage. The counterweight stub arm is most likely held into the bearing cup by a rubber bush and this is most likely fitted under pressure. Perhaps the rubber bush has softened or shrunk and needs replacing. Anyone who services turntables should be able to repair this arm.
  2. The O/P transformer Is for push pull pentode operation of the EL84 with the option of low loading. It is not designed as an ultra linear transformer.
  3. An EL34 draws 1.5 amp of heater current. It would be o.k to wire the valves to the individual 6.3 volt supplies. The operating points for the valve to determine the anode and screen currents has to be taken into consideration as your power transformer has a current rating of 125mA for the B+ supply. This is an old transformer and care has to be taken as the insulation of the windings cannot be assured and running the transformer at full capacity could result in failure. There is no point in running EL34s in an amplifier where the performance has to be restricted to meet the limitations of the power supply and the O/P transformer. This would be an unwarranted design exercise when the Mullard 5/10 amplifier circuit already serves as a guide.
  4. I would suggest that you will not have any trouble staying with the EL84 valve style as an output valve. These are readily available and there are higher rated equivalents such as the Russian type 6P14P that allow a greater power output to be achieved with modifications to the amplifier circuits to make use of silicon diodes in the high voltage supply and the application of fixed bias. The only other valve type that would suit is the 6L6GC beam tetrode as the heater supply current is a modest 0.9 amp which is only slightly higher than that of the EL84. The screen voltage supply needs to be adjusted to suit this valve.
  5. The 'H' does not apply to the OT 2525. It appears that the appropriate valve type was left out of the brochure. The power transformer is in-adequate for push pull operation of EL34 valves and given that all the transformers are from the 1950s caution must be taken as the insulation may not be fully effective.
  6. To add to trobins information; the transformers are designed for the Mullard 5/10 design. That amplifier used 6BQ5/ EL84 valves in a pentode push pull mode. The A & R OT 2525 transformer could be used in the normal or low loading mode. If an amplifier were to be constructed based on this design, some thought should be given to modifying the first valve stage to reduce the high gain to better suit modern source equipment.
  7. A high wattage Variac is the usual method of testing an amplifiers performance at its rated mains voltage. A 'quick check up ' implies that the amplifier was not left with Garry so that a full internal assessment could be carried out. Possibly the covers were not removed so that the filter capacitors could actually be read for values and the rail voltages measured. If you need to check mains voltages and care is needed, a true RMS voltmeter is required and in some circumstances the waveform of the mains supply should be examined on an oscilloscope. In my area the mains is always close to the 240 v specification. When obtaining a replacement transformer , the physical size needs to be checked to make sure it will fit into the available space. What specification, concerning the mains supply and VA ratings are given on the compliance plate of the Parasound amplifier?
  8. Nichicon, Panasonic and Rubycon are all acceptable brands that I would expect to be used by a technician as replacement filter capacitors. Upgrading as such, would be by way of a higher operating temperature ( 105 d ), low ESR and higher voltage and surge current ratings. I would leave the choice to the person that services the amplifier if it is found that they need replacing. The toroidal transformer is the costly part and if it is of the wrong rating , then you have a problem.
  9. Stephenfarbe, you may be confusing the arm cartridge resonance (acr) problem with acoustic isolation. The acr is initiated by ripples in the vinyl surface and in severe cases it can be detected when closely watching the headshell and cartridge vibrating while playing a record.
  10. in terms of the resonant frequency the combination looks o.k. but it is the Q of the resonance which causes trouble and that is the reason for adding damping devices, unless adequate damping is included in the design of the cartridge and of course the arm.
  11. Primare Knob, You may have pointed out a likely problem which is often found with imported equipment and not just the grey candidates. The fitting of power transformers with ratings to suit the Australian mains supply is often overlooked as we are still a miniscule market for high end equipment. Often, despite labelling to the contrary, 220 Volt ac transformers are fitted and consequently filter capacitors are run at higher voltages and this can lead to a reduced service life if the components do not have a sufficient rating to cope with the added stress. Basically the capacitors will operate at a higher temperature and cause higher peak currents to be drawn ( the rectification process causes a spikey current to be drawn through the transformer, not a half sinewave ) and this is ,in part, the cause of the transformer buzz. There is also a problem that toroidal transformers run the cores at higher flux levels for reasons of efficiency vs cost.
  12. What are the make and model of the speakers connected to the PrimaLuna amplifier? Without knowing all the details of the hookup, it is difficult to point to anything as a direct cause, other than a hum loop caused by multiple earthing of equipment. Suspects here are your computer, sources feeding into the computer, the amplifier and possibly the speakers if they incorporate a power supply or use a powered woofer. If the Prima Luna is stock standard and has not been subject to fiddling with different valves then maybe it should be serviced and tested by a technician to ensure it is free from fault. Audible hum from the mains transformer should only be heard when listening within a close distance. Integrated stereo valve amplifiers tend to have higher hum levels on their speaker lines and this is partly caused by internal heater wiring and induced hum coupled into the output transformers via a centrally mounted power transformer.
  13. Perhaps if you listed the model Infinity and the problem that needs fixing, someone might be able to make a recommendation. If the planar drivers (EMIM) require rebuilding then the Apogee Acoustics company is closer to you than Melbourne.
  14. It is not always easy to combine a cartridge with a pickup arm to achieve a well controlled LF performance. Shure and Pickering/Stanton used a hinged stylus brush to limit the problem and the Discwasher company produced a very effective device called the Disctracker as a solution. It is always better to cure the problem at its' source rather than rely on electronic filtering further down the track. This is because an underdamped resonance is also a tracking problem which can increase record and stylus wear.
  15. The agent for the Parasound amplifier is Network Audio Visual in Sydney. Since replacement parts may be needed , it may be wise to make contact and ask them if they have an authorised service centre in Melbourne. There still may be a parts warranty applying for your amplifier if it was originally purchased through an Australian dealer. If this approach proves fruitless, then I would take the amplifier to Garry Cawsey at 41 Edward Street, Brunswick for a test and service to fix the problem.
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