Jump to content
British Coin Forum - Predecimal.com

50 Years of RotographicCoinpublications.com A Rotographic Imprint. Price guide reference book publishers since 1959. Lots of books on coins, banknotes and medals. Please visit and like Coin Publications on Facebook for offers and updates.

Coin Publications on Facebook

   Rotographic    

The current range of books. Click the image above to see them on Amazon (printed and Kindle format). More info on coinpublications.com

predecimal.comPredecimal.com. One of the most popular websites on British pre-decimal coins, with hundreds of coins for sale, advice for beginners and interesting information.

ozjohn

Sterling Member
  • Content Count

    946
  • Joined

  • Last visited

  • Days Won

    25

ozjohn last won the day on April 8

ozjohn had the most liked content!

Community Reputation

342 Excellent

About ozjohn

  • Rank
    ---

Recent Profile Visitors

3,818 profile views
  1. That is the permeability constant ur of magnetic materials change with the current exciting it where as the permittivity of a dielectric remains constant.
  2. That's right I suspect the magnetic materials used in modern speakers is much improved over that used in the 1960s also large speakers were always better for good bass response. I've always liked the idea of electrostatic speakers from the point of view they are linear because the dielectric stays the same with different voltages applied where as magnetic materials change as the current exciting it is changed. Quad brought out some in the late 1950s and still make them to this day along with Vacuum tube amps. They are probably expensive and may be limited in their power handling.
  3. I had a look into the difference between the KT 66 and KT 88 tubes. The KT 88 was an older tube and of a higher power rating than the KT 66. KT 66s were probably used in domestic HiFi amps as 20 watts output power was deemed sufficient as the dynamic range of vinyl LPs was about 45 dB and with an average listening level of about 0.5 w to 1 w the headroom was sufficient to prevent excessive distortion. There were also a lot of power amps based on the Wireless World Williamson amplifier that delivered 10 w output power using EL 84 tubes in push pull. Most modern domestic HiFi amps are in excess of 50 w output power to accomodate the much increased potential dynamic range of 100 dB offered by CD and other digital streaming as the dynamic range is determined by the number of quantisation levels during digitisation rather than a voltage level or the distance a stylus can travel on a vinyl record.
  4. Very nice coin but I feel sorry for the horse, he has a very sad face.
  5. My Grandfather had a pewter tankard with a glass bottom. On the glass bottom there was a picture of a man on the gallows and an inscription, "Good to the Last Drop."
  6. Impressive setup. I'm afraid I like math approach. Yes the KT66 was the lower power tube while the KT 88 was a higher power device. KT stands for kinkless tetrode .
  7. They both came from the same seller.
  8. My latest coin one of the harder dates of the Edward series. All I need is a high grade 1905 florin at a good price. I live in hope. I notice that Britannia's face seems worn but in the hand it's pretty good.
  9. My latest penny. Not a rare date but but a nice example.
  10. Yes I met Small when I was working at Sydney Uni. Small signal analysis is where you linearize a nonlinear transfer function around an operating point and is much used in electronic circuit design. I can also remember Goodmans suggesting that you mounted speakers in a concrete column. I have never seen any analysis of this but I suspect it would involve circular harmonics leading to Bessel's partial differential equations . Any relation of small signal to Richard Small is incidental as small signal analysis was used mainly in electronic circuit design to accommodate the non linear nature of vacuum tubes, FETs and BJTs. I'm afraid my audio is entirely shop brought with a Denon AVR X250BT 5.1 tuner amp and Wharfedale Alantic SE Series speakers 2 AT-400 SE and 2 AT200 SE. The Denon employs a white noise source to balance the speakers but does not support a microphone like the earlier Denon I had so I use a sound level app on my phone that seems to deliver reasonable results. I changed the earlier Denon as it did not support 4k HDMI. Earlier on in my career I worked at the MO Valve company where they made the KT 88 and KT 66 tubes. not realizing that they would be sought after today by some audio buffs who want to chase the Vacuum tube sound.
  11. Hot Cross buns one a penny two a penny.
  12. Thiele, A. N., "Loudspeakers in Vented Boxes: Parts I and II," J. Audio Engineering Soc., Vol. 19, No. 5, May 1971, pp. 382–392 (Reprinted from The above paper may be of interest if you are technically minded. It describes the design of bass reflex enclosures using second order control theory. I think audio reproduction has been revolutionised in recent years by the use of adaptive equalisers in tuner amplifiers where the response of the venue is scanned and the frequency response of the system adjusted accordingly. Using this very ordinary speaker systems can produce high quality results. I first saw this demonstrated when I was a student where students had to present a project as part of their course work to their fellow students and academics.
  13. ozjohn

    1917 Sixpences Grading

    Sorry about the 1976 error a silly typo.
  14. ozjohn

    1917 Sixpences Grading

    Check out this 1976 sixpence on Ebayhttps://www.ebay.co.uk/itm/1917-Great-Britain-6-Pence-PCGS-MS-66-Sixpence/173568759924?hash=item2869811874:g:eIsAAOSw9w1btBPg and PCGS https://www.pcgs.com/cert/34024776 It's nothing on ypur one.
  15. ozjohn

    1917 Sixpences Grading

    Like the other posts I have difficulty in grading early George IV silver coins. When all else fails I suggest examination of the milling as that always seems to be deeply struck and an early indication of wear.
×