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Thread: Hammond E series Choke

  1. #21
    p Piano geoffbrown's Avatar
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    Installing a 1A fuse in the primary side of the transformer will give little protection against any future meltdown.

    The secondary outputs of the power transformer need to be individually fused, to give maximum circuit protection ,for example use 250ma fast blow fuses on the HT leads and slow blow fuses on the heater leads.

    Like you I find replacement transformers and chokes for 50 plus year old equipment extremely expensive and hard to come by, so it makes sense to install extra fuses which weren't installed at the time of manufacture, but now would be mandatory

  2. #22
    fff Fortississimo David Anderson's Avatar
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    1 members found this post helpful.
    Quote Originally Posted by geoffbrown View Post
    Installing a 1A fuse in the primary side of the transformer will give little protection against any future meltdown.

    The secondary outputs of the power transformer need to be individually fused, to give maximum circuit protection ,for example use 250ma fast blow fuses on the HT leads and slow blow fuses on the heater leads.
    Geoff,

    As someone who's been working on tube amps for 25 years and who owns over 20 pieces of vintage tube gear, I would disagree with this assessment.

    I've seen countless amps that were saved from catastrophic damage by fuses on the primary side of the power transformer. The vast majority of cases where this doesn't work are where someone has responded to a blown fuse by installing a larger one. I have a collection of 20A fuses pulled from amps.

    Fusing the B+ is an extra step that can be reasonable, especially in amps where the output tubes tend to be abused, but I'm on a professional tech group, including many amp builders, and the overwhelming consensus is that fusing heater secondaries has more downsides than benefits. I don't think I've ever seen a situation where a heater secondary fuse would have saved a transformer. The only reasons that some current-production amps have fused secondaries is European hyper-regulation of anything electronic, brought to you by the same folks who were going to insist that all electronic equipment be designed with timers to switch it off after a certain time period -- because we all want our amps to switch themselves off in the middle of a solo.

    By far the best way to save your equipment is to have the necessary preventive maintenance done before something blows up. I understand that people want their amps to last a long time, but, at the same time, on this forum, we have a lot of folks doing this work themselves when it's glaringly obvious that they are in way over their heads in terms of understanding what they're doing. Equipment seriously damaged by owner/tinkerer-error arrives on my bench all the time. Having people not attempt repairs and restorations that they're not qualified to do would in and of itself greatly reduce damage; yet some of us encourage and enable it.

    It's not all that unusual for power transformers simply to fail on their own because there was some flaw in construction or -- more often -- the manufacturer chose an inadequate power transformer for the application. There are certain Fender amps where it's common to find a blown power transformer. There's little you can do about that except in cases where someone is offering a power transformer upgrade. That's why my Dynaco ST-70 has the Triode Electronics upgrade PT. It runs much cooler than the original.

    When it comes to the E-100, I'm not an expert on them, but it seems that the chokes are prone to failure. That points to a design miscalculation because chokes rarely fail. The same is true of transformers in Leslie 25 and 125 amps.
    I'm David. 'Dave' is someone else's name.

  3. #23
    ppp Pianississmo jakobsongs's Avatar
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    Ok, firstly a big thanks to all that have been helping me, I now have a new choke installed, voltages are much better than they were, but I'm still 25V over at the 450V tap after the choke, is this likely to cause a problem? I played it for a while, and transformer and choke were just slightly warm.

  4. #24
    mf Mezzo-Forte Roger Memphis's Avatar
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    Quote Originally Posted by jakobsongs View Post
    I'm still 25V over at the 450V tap after the choke, is this likely to cause a problem? I played it for a while, and transformer and choke were just slightly warm.
    Warm is good! (Hot, not so much ). 25 V is only about 5.5% over... I wouldn't worry about it. Glad you got 'er working !
    Roger Memphis
    C-3 with O-M, 145, 122RV, 2 PR-40's, PSR-36
    CV with HR-40, 2 B-40's

  5. #25
    ppp Pianississmo jakobsongs's Avatar
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    Thank you, that's great news, now to get the reverb working! I've already changed around 75% of resistors, so think I just as well change the lot whilst solving the reverb problem.

  6. #26
    Moderator Wes's Avatar
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    Make sure you are not right at (or over) the limit of your B+ filter caps, and you should be fine. 5% over can simply be the result of a high mains voltage. The schematic specs them for 117V mains.

  7. #27
    ppp Pianississmo jakobsongs's Avatar
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    Quote Originally Posted by Wes View Post
    Make sure you are not right at (or over) the limit of your B+ filter caps, and you should be fine. 5% over can simply be the result of a high mains voltage. The schematic specs them for 117V mains.
    Ok thanks, all seems well below their 500V rating.

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