[Heath] Fwd: Fwd: Final transistors for SB 104A
Chris Iwata
chrisiwata at aol.com
Fri Sep 24 17:40:23 EDT 2021
Well, we're off topic now. This thread was supposed to be about the
SB104 finals
To be fair, those MFC6030 ICs failed due to domino effect.
In both the SB104 and HP1144 regulator circuits, the IC current capacity
was boosted by a pass transistor. The transistor failed, leading to
failure of the IC. The transistor failed from something connected to
the regulator circuit drawing too much current.
In the power supply case, this was dangerous. The transistor shorted
out. Instead of 13.8v going to the SB104, if there was no crowbar, it
would have been around 20v.
In the SB104 the voltage to the digital ICs was too high, so they drew
more current. It needed to be 4.75v to 5.25v. But because of 10%
resistor tolerances it was higher. So the transistor overheated.
Luckily, in this instance the transistor open circuited, so the
regulator output voltage went to zero.
Chris, KL7DM
On 9/22/2021 8:49 PM, Steven Feinsmith wrote:
> Thank you, Chris, for clearing this up for me about the MFC6030A
> voltage regulator by Motorola. Also, you are correct that the HP-1144
> power supply had no crowbar to protect the transceiver included
> SB-634, SB-644A, and SB-614 through power chain links. The HP-1144A
> had an improved design including a crowbar circuit.
>
> The price for MFC6030A went up crazy price at:
>
> https://store.americanmicrosemiconductor.com/mfc6030a.html
> <https://store.americanmicrosemiconductor.com/mfc6030a.html>
>
> Fortunately, my HP-1144 is working except for my concern with a pair
> of filter capacitors because the top terminals were not flat. I do not
> know if it is normal because I did not have another HP-1144 or
> HP-1144A for comparison. I plan to pull out both filter capacitors to
> test for leakage and find their capacitance range to ensure that they
> are ok or not. Secondly, I plan a test ripple from them and use my
> infrared image gun to see thermal reading for abnormal.
>
> Nowadays, it has become more difficult to buy large capacitors because
> many companies are no longer in stock because of the pandemic
> incidents. All vendors jacked up the price into unreasonable costs for
> the replacement. That is why I got a switching power supply designed
> for the Ham radio system to replace the H-1144 in the SB-604 chassis.
> The advantage of the switching power supply is that it is much lighter
> in weight and smaller physically with a cooling fan. The device has
> built-in overvoltage and overcurrent protection with adjustable
> voltage and noise. The device is a TekPower TP30SWV 30 Amp DC 13.8V
> Digital Switching Power Supply with Noise Offset.
>
> I know many Heathkit items need new parts replaced but are no longer
> available. So many Heathkit items posted on eBay could be around 90%
> not working while sellers want for hundred of dollars and said, they
> applied the power and it on. That is all. That was not correct how
> they tested the equipment before selling it to buyers. Can we buy a
> non-working car at a price that is supposed to be a working car? Of
> course, no! That problem with sellers and eBay. Fortunately, I have
> experience in electronics and can repair anything even if I have to
> change the design to replace non-available components.
>
> It was not Heathkit's fault because they did not know what the future
> would be. The problem is electronic component manufacturers like
> Motorola, Texas Instruments, Emiac, and many others enjoy
> discontinuing the products and allow many people to cry and face jack
> up the prices as much as gold prices.
>
> Thank you very much,
> Steven
>
>
>
> On Wed, Sep 22, 2021 at 10:32 PM Chris Iwata <chrisiwata at aol.com
> <mailto:chrisiwata at aol.com>> wrote:
>
>
> When I mentioned restoring the SB104 that meant bringing it back
> to as originally sold. No workarounds.
>
> The MFC6030 voltage regulator IC in the SB104 is the same as in
> the HP1144 power supply. On my SB104 it failed, and the one in the
> power supply also failed. This is a 4 terminal regulator no longer
> in production and only Motorola made it. I couldn't even find an
> NTE replacement. ICs theoretically last almost forever, but
> practically they don't. Ultimately I used a 7805K for the SB104
> and completely redid the power supply using a LM723 regulator.
>
> The computer grade cap in the power supply used to be cheap as
> surplus when computers used TTL ICs. but no more. The one in my
> power supply failed also. The 1144 power supply I own had no
> crowbar overvoltage protection, I added it myself. This was added
> in 1144A version. This is very important if you want to protect
> your SB104 from disastrous failure.
>
> One final RF transistor blew. This happened from high VSWR.
> Rather than buying a matched pair or quad, I redid the final to
> use only 2 transistors at reduced wattage.
>
> Chris, KL7DM
>
> On 9/22/2021 4:51 PM, Steven Feinsmith wrote:
>> First of all, both SB-104, SB-104A, and SB-230 are not dying. The
>> 2N6456 RF transistors have indeed become more difficult to find
>> nowadays. The greedy eBay sellers pumped for around 100 dollars
>> each. Of course, no one is buying 400 dollars. There is a big
>> issue about whether a matched quads may be impossible. I did
>> mention in my previous message that I should buy an old rig that
>> uses the 2N6456.
>>
>> The same problem with SB-230 uses a 1KW tube that was no longer
>> stock and depleted from the vendor's inventory.
>> Some Ham users use Russian-made microwave tubes to take over with
>> some modifications.
>> The front panels use a Panaplex display. It is a gas discharge
>> display that was very popular and easy to read. There was a
>> slight problem with the Panaplex because it requires 180 volts to
>> run the gas discharge. It tended to give out some electrical
>> noise. There are articles about converting Panaplex to LED for
>> both SB-634, station, and SB-104A, transceiver.
>>
>> Now, I am working on a new PCB for the SB-104A display to run
>> with the LED instead of Panaplex.
>>
>> The problem is with the new ham radio transceivers that
>> physically shrink a lot, but it had many features, such as
>> digital modes with USB ports. The amplifier tends to use
>> high-power transmitting tubes now as MOSFET. The price tag, OUCH!
>> I am poor as a retiree and earn a social security retirement
>> check every month.
>>
>>
>> You mentioned voltage regulators. My SB-104A is running fine as a
>> licensed operation tested them. I checked everything with my
>> DMM/VTVM to ensure voltages are within specification. Can you
>> explain the details about the voltage regulators. I also found my
>> HP-1144 power supply seems to have two filter capacitors that may
>> need replacement. The cost is crazy as I bought a switching power
>> supply that provides matched voltage and provides 30A instead of
>> 20A with overvoltage and overcurrent protection. The advantage
>> with the switching power supply was that it was very light
>> compared with a massive transformer's weight.
>>
>> Just try to keep Heathkit alive ahead of time!
>> Steven
>>
>>
>> -------- Forwarded Message --------
>> Subject: Re: [Heath] Fwd: Final transistors for SB 104A
>> Date: Wed, 22 Sep 2021 12:56:01 -0700
>> From: Chris Iwata <chrisiwata at aol.com>
>> <mailto:chrisiwata at aol.com>
>> To: ka9dzr at aol.com <mailto:ka9dzr at aol.com>
>>
>>
>>
>>
>> If you luck out and find some, bear in mind that you have to
>> buy matched pairs.
>>
>> Theoretically, you have to buy matched quads. But you can
>> probably be OK with matched pairs
>>
>> Expect to pay a premium, those stud mount RF transistors
>> haven't been made for at least 20 years. A guess would be at
>> least $50 each
>>
>> Your best bet is to buy a junked SB104
>>
>> The SB104 will become unrestorable due to unavailability of
>> the Final transistors, the Nixie tubes, the Nixie driver IC,
>> and the voltage regulator IC.
>>
>> Chris, KL7DM
>>
>>
>>
>> On 9/22/2021 10:18 AM, ka9dzr--- via Heath wrote:
>>> has anyone fine any replacement finals for the sb-104a yet
>>> tnx ka9dzr Dennis
>>>
>>> ------------------------------------------------------------------------
>>> From: heath at puck.nether.net <mailto:heath at puck.nether.net>
>>> To: heath at puck.nether.net <mailto:heath at puck.nether.net>
>>> Sent: 11/24/2014 4:56:23 PM Central Standard Time
>>> Subject: [Heath] Final transistors for SB 104A
>>>
>>> I have learned that the 2n6456 final RF transistors are
>>> no longer available and I NEED to replace the four (4)
>>> in a Heath SB 104A. Has anyone found a suitable
>>> replacement transistor for this application? I have
>>> thoroughly checked with RF Parts and they no longer
>>> stock those transistors.
>>> Does anyone have experience substituting the final
>>> transistors in the SB 104A? If so what did you use as a
>>> replacement and do you know where they can be found?
>>> Thanks and 73, John, K5PGW
>>> _______________________________________________
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