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eHam Forums => Amplifiers => Topic started by: KW4GT on November 09, 2017, 05:33:53 AM



Title: New SB-221 build - what mods are recommended?
Post by: KW4GT on November 09, 2017, 05:33:53 AM
I've got a partially completed SB-221 (including all the original parts from the kit) which I purchased quite some time ago.  It looks like I'm finally going to be able to get around to finishing it sometime in the next several months - what mods would you guys recommend and are there any that should be avoided?  (It already has the 10 meter parts installed).

ALSO... I've seen many folks refer to "Harbaugh" kits, but a quick search only yielded "Harbach Electronics"..... can I assume that somewhere along the way somebody misspelled it and everyone else followed suit or are the two actually separate entities?



Title: RE: New SB-221 build - what mods are recommended?
Post by: W1QJ on November 09, 2017, 05:58:15 AM
Yes, the name was misspelled, the correct spelling is Harbach.  When you added the 10 meters, was that from a factory supplied kit with factory instructions?  This is important, that is why I asked.  As far as "mods".  Since you are at this point you might want to consider installing these three Harbach kits.  1. A MUST will be the soft key!!!  This is without doubt. 2. Second consideration would be rectifier board kit, Not a must like the soft key but it does have the following that  the original board does not have, 3 amp didoes, meter protection, eliminates the zener diode.  Many amps are out there with stock boards but consider the benefits.  Lastly the capacitor bank.  The old caps are probably ok but new ones might be a consideration.  Not a bad idea. 

Some say a soft start but the transformer is designed to not need one at stock filter capacity.  Once again, can't hurt if you want to spend the money.


Title: RE: New SB-221 build - what mods are recommended?
Post by: KW4GT on November 09, 2017, 06:09:21 AM
The 10 meter parts were already installed when I bought the unfinished project, I believe they're factory parts.  I didn't get instructions, but have been able to find them online.


Title: RE: New SB-221 build - what mods are recommended?
Post by: W1QJ on November 09, 2017, 06:30:33 AM
The 10 meter parts were already installed when I bought the unfinished project, I believe they're factory parts.  I didn't get instructions, but have been able to find them online.

OK, just wondering, I'll assume the 10 meter kit was bought at time of purchase or thereafter and was assembled properly.  The 10 meter kit came with everything needed and instructions.  They are no longer available and adding 10 meters to an already built SB-221 isn't an easy task at all.  It is much easier to obtain a completed SB-220 network with 10 meters and just drop it in as mostly a mechanical change over with limited soldering and effort compared to trying to rebuild an SB-221. 

Have you made up your mind on what mods you want?


Title: RE: New SB-221 build - what mods are recommended?
Post by: K1ZJH on November 09, 2017, 07:21:49 AM
Soft start will protect the power switch contacts, but since the amp has never been used it probably has thousands of hours left on its contacts.  I used one since my SB-220 was ancient when I did a total rebuild. One consideration is that it also adds one more thing that can fail and go wrong.

Avoid any improvements  that include the word Nichrome!

One more suggestion is to add a glitch resistor. That is cheap insurance. There is an Ohmite resisor
that is designed to withstand high peak current discharges,  I don't recall the part number offhand,
perhaps Lou or someone else has that info handy... or just look at a MFJ amp, most use them.

Pete


Title: RE: New SB-221 build - what mods are recommended?
Post by: K0BT on November 09, 2017, 08:08:40 AM
I built mine a few years ago and added a vacuum relay and transistor switching to make it compatible with newer rigs. 


Title: RE: New SB-221 build - what mods are recommended?
Post by: KW4GT on November 09, 2017, 09:39:38 AM


Have you made up your mind on what mods you want?

Well, I'm hoping for some input as far as which ones make the most sense.  It looks like the only Harbach mod that's really a necessity is the "Soft Key" interface since I now have a solid state rig.

Will a "Soft Start" module gain me anything?  I've read that Heathkit sized the transformer of the SB-220/221 to naturally limit inrush current. 

Also, what advantages would the Harbach Rectifier/Metering Board or Filter Capacitor Block offer over the unused originals that I now have?

thanks



Title: RE: New SB-221 build - what mods are recommended?
Post by: W1QJ on November 09, 2017, 01:35:18 PM
I covered the pro’s of the rectifier board.  Go back and look.  You are right about the transformer limiting.  New caps is a plus over the old ones sitting unused for many years.  With the cap bank you get smaller resistors with less heat.  Glitch resistor ok but the grid shunt resistor is a special one that blows open like a fuse on a glitch.


Title: RE: New SB-221 build - what mods are recommended?
Post by: KW4GT on November 09, 2017, 09:48:41 PM
Another question.... Are the capacitors in the replacement filter kit the same value as the originals? 


Title: RE: New SB-221 build - what mods are recommended?
Post by: W1QJ on November 09, 2017, 10:01:45 PM
Another question.... Are the capacitors in the replacement filter kit the same value as the originals? 

Yes, I believe they are 220UF or thereabouts.  Anything will work to a point. The ideal capacitance is around 32uf total.  220/8=~27uf so close enough.


Title: RE: New SB-221 build - what mods are recommended?
Post by: WA7PRC on November 10, 2017, 12:37:31 AM
I built mine a few years ago and added a vacuum relay and transistor switching to make it compatible with newer rigs.  
This is a good idea. The vacuum relay (output switch) and a reed relay (input switch) will eliminate "hot switching" and intermittent oxidized amplifier relay contacts. The W7RY board adds electronic bias regulation and switching. The board is easy to assemble, and Jim offers a suitable reed relay.

The OE SB-220 rectifier/meter board can be upgraded for a fraction of the cost of the H*rbach RM-220...
- Replace rectifiers w/ 1N5408s (3A/1KV) for pennies each.
- Replace 4M7/1W carbon composition HV meter multiplier resistors w/ HV-rated MOX resistors for pennies each.
- Add AT LEAST 3A (200A pulse) rectifier between -B and chassis to protect meters from HV fault. A 6A (400A pulse) rectifier is safer and only a few pennies more.
- If/when the 5V/10W Zener goes, replace w/ a stack of inexpensive rectifiers (or better yet, the W7RY board).


Title: RE: New SB-221 build - what mods are recommended?
Post by: KM1H on November 10, 2017, 07:26:35 AM
Quote
The OE SB-220 rectifier/meter board can be upgraded for a fraction of the cost of the H*rbach RM-220...
- Replace rectifiers w/ 1N5408s (3A/1KV) for pennies each.

The PC board holes need to be drilled out a bit, use a correct size sharp drill as there is little room to spare on the traces.

Quote
- If/when the 5V/10W Zener goes, replace w/ a stack of inexpensive rectifiers (or better yet, the W7RY board).

Unless QSK is needed that board and associated parts you have to buy is expensive overkill. Old stock relays slow down with age and are readily available for around $10 from Mouser, etc.
The better rigs allow TX/RX timing to be matched to the relay speed and thats good for regular 30-35 WPM + VOX type CW operation. I havent needed anything fancy in 50+ years.


Title: RE: New SB-221 build - what mods are recommended?
Post by: K8AXW on November 10, 2017, 08:45:39 AM
GT:  I recommend you complete the kit (with the new filter caps as others have recommended) and get it working before you start modifying it!

THEN, after you get the amp working as specified, consider these suggestions listed above.

No doubt by the time this is over the "mod list" will have grown and shrunk many times.

Final point:  There is nothing more frustrating than trying to troubleshoot a sick piece of gear after it has been modified to hell and gone!



Title: RE: New SB-221 build - what mods are recommended?
Post by: K1ZJH on November 10, 2017, 09:27:51 AM
They did work, and quite well, from the factory as designed.  But the softkey mod may be needed to interface to some newer rigs.


Title: RE: New SB-221 build - what mods are recommended?
Post by: WA7PRC on November 10, 2017, 09:36:00 AM
This is a good idea. The vacuum relay (output switch) and a reed relay (input switch) will eliminate "hot switching" and intermittent oxidized amplifier relay contacts. The W7RY board adds electronic bias regulation and switching. The board is easy to assemble, and Jim offers a suitable reed relay.
Quote
Unless QSK is needed that board and associated parts you have to buy is expensive overkill. Old stock relays slow down with age and are readily available for around $10 from Mouser, etc.
The better rigs allow TX/RX timing to be matched to the relay speed and thats good for regular 30-35 WPM + VOX type CW operation. I havent needed anything fancy in 50+ years.
The main reasons are to get rid of "hot switching" and increase reliability with hermetically-sealed relay contacts. QSK function is a side benefit. In addition to giving you adjustable electronic operating bias, the W7RY board also eliminates relay contacts for switching between operating and cutoff bias. For the spendthrift ham, a second set of reed relay contacts can be used instead. There's no need to use a Band Aid by delaying RF (and not all current and existing rigs can do that). The worst-case vacuum/reed relays toggle in about 1ms while the fastest a rig can produce RF is about 5ms.


Title: RE: New SB-221 build - what mods are recommended?
Post by: WE6C on November 10, 2017, 11:12:41 AM
This is a good idea. The vacuum relay (output switch) and a reed relay (input switch) will eliminate "hot switching" and intermittent oxidized amplifier relay contacts. The W7RY board adds electronic bias regulation and switching. The board is easy to assemble, and Jim offers a suitable reed relay.
Quote
Unless QSK is needed that board and associated parts you have to buy is expensive overkill. Old stock relays slow down with age and are readily available for around $10 from Mouser, etc.
The better rigs allow TX/RX timing to be matched to the relay speed and thats good for regular 30-35 WPM + VOX type CW operation. I havent needed anything fancy in 50+ years.
The main reasons are to get rid of "hot switching" and increase reliability with hermetically-sealed relay contacts. QSK function is a side benefit. In addition to giving you adjustable electronic operating bias, the W7RY board also eliminates relay contacts for switching between operating and cutoff bias. For the spendthrift ham, a second set of reed relay contacts can be used instead. There's no need to use a Band Aid by delaying RF (and not all current and existing rigs can do that). The worst-case vacuum/reed relays toggle in about 1ms while the fastest a rig can produce RF is about 5ms.

Bryan, What would be the ballpark cost for these relays?
Bob


Title: RE: New SB-221 build - what mods are recommended?
Post by: K0BT on November 10, 2017, 01:10:59 PM
Definitely keep drawings of anything you do.  It's disconcerting when you can't remember the details just two years later.


Title: RE: New SB-221 build - what mods are recommended?
Post by: KW4GT on November 10, 2017, 06:33:06 PM
Definitely keep drawings of anything you do.  It's disconcerting when you can't remember the details just two years later.

Sounds like you're speaking from experience. 8)