[Heath] Fwd: Fwd: Final transistors for SB 104A

Fri Sep 24 20:23:22 EDT 2021

Thank you, Chris, for the information. I have Heathkit SB-104A as the final
amplifier. I nervously learned my HP-1144 power supply was designed without
a crowbar circuit. I believe Heathkit realized and redesigned the HP-1144
to become HP-1144A. There is a company that provided piggyback PCB for the
HP-1144 with a crowbar circuit. My power supply has a pair of large filter
capacitors. It showed me that the terminals were not flat but looked like a
"dome." I did not know if this was normal or not. I forced myself to get a
switching power supply to take over.

I notice transceivers tend to lack a protection circuit for the final or
power RF transistors as same with vacuum RF power  tubes from overcurrent
or overvoltage that are sure way to destroy it as same with heat.

My SB-104A has external cooling fans attached to the heatsink and also
thermal sensors to watch out from overheating. Now, I am thinking about
creating a new circuit to find a way to protect the RF transistors by
restricting current and voltage.

Steven

On Fri, Sep 24, 2021 at 5:40 PM Chris Iwata <chrisiwata at aol.com> wrote:

>
> 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
>
> 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> 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> <chrisiwata at aol.com>
>>> To: 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
>>> To: 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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>>
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