Radio Shack/Grommes LJ-5?

[Derek G]

Hello,

I'm newer to these forums. Thank God for AK. I've spent the past six months diagnosing and restoring a few Marantz units. I've learned quite a bit about solid state with much help. So. Here I am. Seeking more input. I have no knowledge in Tube Audio. But I'm very curious. Everybody has to start somewhere right? Today was a good day. I acquired a mono Realist (Radio Shack Boston) amp. Cleaning out a garage. It was given to me. Unbeknownst of any working condition. I couldn't wait to come home and investigate. This lil guy cleaned up really well. I hooked it up to my dim bulb and she appears good. All the tubes fire. Anyways. I googled it up. Finding its a LJ-5. Originally a Grommes LJ-5 rebranded by the Shack. Correct me if I'm wrong. I realize this is a single mono unit and to acquire "stereo" I will need a twin. So. How do I move forward? I wouldn't mind using this amp to listen to am "mono" channels with a single speaker hooked up to a time similer speaker. How do I test this amp? Can I use one channel from a pre amp output on a receiver? Also. How do I wire a speaker to it? It has four posts. C/4/8/16. I'm assuming 4/8/16 are ohms. What is C? Do I need a speaker with 1 wire? Any help would be very appreciated. See pics. I would love to hear this thing sing. Also. Everything looks great inside but.... Do I need to recap or replace anything moving forward. Thanks in advance. View attachment 1385788

 

[Tom Bavis]

Yes, you can connect it to a preamp out for testing, or to a source like a CD player or PC audio (RADIO input). CONNECT A SPEAKER before you connect any input - tube amps can be VERY unhappy (involving SMOKE!) if driven without a speaker. "C" is the "Common" speaker terminal, speaker hooks from "C" to "8" if it's 8 Ohms etc.

Grommes did include a FUSE in their design, though I don't see one - looks like RS saved a few cents! Voltage tests are a good idea. ANY positive voltage at pin 5 (the grid terminal) of the 6V6 tubes is a sign of a leaky cap and a sign that that 6V6 won't last long! Schematic with voltages is on my web page: http://www.audiophool.com/hifistuff.html If you don't have a voltmeter, it's 5 bucks at Harbor Freight and well worth the time learning to use it.

 

[Lavane]

I have what's left of that same exact amp. It just said "Hi-Fi" on the gold face plate with a big V under that. Someone else posted about this amp some time ago under yet another brand name. I used mine for years with an Eiko mono tube tuner in my garage.

 

[Derek G]

Yes, you can connect it to a preamp out for testing, or to a source like a CD player or PC audio (RADIO input). CONNECT A SPEAKER before you connect any input - tube amps can be VERY unhappy (involving SMOKE!) if driven without a speaker. "C" is the "Common" speaker terminal, speaker hooks from "C" to "8" if it's 8 Ohms etc.

Grommes did include a FUSE in their design, though I don't see one - looks like RS saved a few cents! Voltage tests are a good idea. ANY positive voltage at pin 5 (the grid terminal) of the 6V6 tubes is a sign of a leaky cap and a sign that that 6V6 won't last long! Schematic with voltages is on my web page: http://www.audiophool.com/hifistuff.html If you don't have a voltmeter, it's 5 bucks at Harbor Freight and well worth the time learning to use it.

I will do some voltage checks in the morning. She seems to be running pretty good. Crystal clear sound...

 

[Derek G]

I pulled out my old VCR and and ran an audio output. I hooked an 6ohm onkyo surround test speaker I use. Bam! She sounds wonderful. I'm listening the The Dark Crystal. I must admit. This is very satisfying. I cleaned all the pots up with dioxit. Everything internally appears good. How hot do these tubes usually run? I have no experience. I know they will burn you to the touch. Is this normal? The 6V6 has almost a blue glow and seems to run the hottest. I've had it up and running for an hour and no issues thus far. Please advise me to all and any servicing I might do to assure safe listening. Thank you.

 

[Big Harry]

I would recommend replacing the coupling caps along with the electrolytic caps to ensure reliability. Those pink Tiny Chief caps are guaranteed to be electrically leaky along with the probability Budroc cap isn't in much better shape either. Replacement caps are not expensive and well worth the effort it takes to replace them. Please keep in mind that you are working with potentially lethal voltages in the range of 300 volts when working on tube equipment and electrolytic caps can hold their charge for a long period of time.

 

[Derek G]

I would recommend replacing the coupling caps along with the electrolytic caps to ensure reliability. Those pink Tiny Chief caps are guaranteed to be electrically leaky along with the probability Budroc cap isn't in much better shape either. Replacement caps are not expensive and well worth the effort it takes to replace them. Please keep in mind that you are working with potentially lethal voltages in the range of 300 volts when working on tube equipment and electrolytic caps can hold their charge for a long period of time.

Thanks for the reply. I'm replacing all the films/electro's you have suggested. Going with cornell dubilier. Also, what's the best way to de-charge this unit before soldering in the new caps. Keep it unplugged for several days? Remove the tubes? Thanks in advance for your time...

 

[Retrovert]

Also, what's the best way to de-charge this unit before soldering in the new caps. Keep it unplugged for several days? Remove the tubes? Thanks in advance for your time...

Removing the tube has no effect because the unit isn't powered, and that, in any event, couldn't discharge capacitors.

Besides, pulling tubes is risky as it causes the power supply to become unloaded and the voltage can increase, particularly in choke supplies where it may rise to 1.4 times the nominal AC secondary voltage, instead of the 0.9.

The phrase for which to search is "capacitor soakage" or "capacitor dielectric absorption". The charge may remain for weeks, months, even years. It has to do with dipoles trapping electrons.

A bleeder resistor connected across the large filter capacitors will safely discharge most of the stored charge, but not necessarily all of it, as per the above. Shorted capacitors regain charge over time as the electrons migrate to the plate surface. The screwdriver technique for discharge is poor as general practice, as it creates great stress in capacitors and can warp the plates; obviously not a concern in a unit where the capacitors are garbage, of course.

Make sure no path for current exists through you when you perform such discharge.

 

[Derek G]

Removing the tube has no effect because the unit isn't powered, and that, in any event, couldn't discharge capacitors.

Besides, pulling tubes is risky as it causes the power supply to become unloaded and the voltage can increase, particularly in choke supplies where it may rise to 1.4 times the nominal AC secondary voltage, instead of the 0.9.

The phrase for which to search is "capacitor soakage" or "capacitor dielectric absorption". The charge may remain for weeks, months, even years. It has to do with dipoles trapping electrons.

A bleeder resistor connected across the large filter capacitors will safely discharge most of the stored charge, but not necessarily all of it, as per the above. Shorted capacitors regain charge over time as the electrons migrate to the plate surface. The screwdriver technique for discharge is poor as general practice, as it creates great stress in capacitors and can warp the plates; obviously not a concern in a unit where the capacitors are garbage, of course.

Make sure no path for current exists through you when you perform such discharge.

Thank you.

Should I replace the large canister capacitor as well or do they usually fair ok? Its a Mallory FP 40/30/10/20. I was told a 40/40/20/20 would suit just fine. Is this ok? Ty.

 

[Big Harry]

A 40/40/20/20 electrolytic cap will be good for your amp. I use a 15K 1 watt resistor with a couple of jumper leads attached to discharge caps as it is much better than using a screw driver to do the job. I buy some of my caps especially the can electrolytics from Antique Electronic Supply in Arizona, but there is also Hayseed Hamfest that can make electrolytic caps up for you. I don't trust old electrolytic caps to be any good after several decades, but they can be tested with an old style cap tester such as a Sprague TO6 that can supply the high voltage necessary to test the caps at their working voltage. Don't get crazy with the coupling caps as anything you use for replacements are better that the originals. My preference for amplifiers are the Orange Drop 715P or 716P caps that are readily available for a reasonable price and work well. Also be sure to test and replace all of the resistors that are out of tolerance as the carbon composition resistors have a tendency to drift high over the years.

 

[Derek G]

A 40/40/20/20 electrolytic cap will be good for your amp. I use a 15K 1 watt resistor with a couple of jumper leads attached to discharge caps as it is much better than using a screw driver to do the job. I buy some of my caps especially the can electrolytics from Antique Electronic Supply in Arizona, but there is also Hayseed Hamfest that can make electrolytic caps up for you. I don't trust old electrolytic caps to be any good after several decades, but they can be tested with an old style cap tester such as a Sprague TO6 that can supply the high voltage necessary to test the caps at their working voltage. Don't get crazy with the coupling caps as anything you use for replacements are better that the originals. My preference for amplifiers are the Orange Drop 715P or 716P caps that are readily available for a reasonable price and work well. Also be sure to test and replace all of the resistors that are out of tolerance as the carbon composition resistors have a tendency to drift high over the years.

Perfect. Ty for your time and input.

 

[Derek G]

A 40/40/20/20 electrolytic cap will be good for your amp. I use a 15K 1 watt resistor with a couple of jumper leads attached to discharge caps as it is much better than using a screw driver to do the job. I buy some of my caps especially the can electrolytics from Antique Electronic Supply in Arizona, but there is also Hayseed Hamfest that can make electrolytic caps up for you. I don't trust old electrolytic caps to be any good after several decades, but they can be tested with an old style cap tester such as a Sprague TO6 that can supply the high voltage necessary to test the caps at their working voltage. Don't get crazy with the coupling caps as anything you use for replacements are better that the originals. My preference for amplifiers are the Orange Drop 715P or 716P caps that are readily available for a reasonable price and work well. Also be sure to test and replace all of the resistors that are out of tolerance as the carbon composition resistors have a tendency to drift high over the years.

Also, what is the polarity on the tiny chiefs? Is the stripe side negative or are they bi polar?

 

[Big Harry]

I have a couple of the smaller amps like yours that use 6V6's for the output tubes. One is an old Pilot and the other is a National Kit. The Pilot is a nice sounding amp due to the large output transformer and the National Kit is an okay performer. I buy my caps from Antique Electronic Supply, Just Radios and Mouser. I haven't bought into the theory that the boutique caps are necessary in old amplifiers as I can't justify the price for what is supposedly gained by using them. Even the yellow mylar caps that are very inexpensive will do a good job in your amp along with either carbon film or metal film resistors which are also inexpensive. There is no need in my opinion to try to source NOS carbon comp resistors for most restorations.

 

[Big Harry]

The band on the Tiny Chief denotes the foil side of the cap. The replacement caps will not have any marking as to outside foil as it isn't a problem and can be installed in most cases in either direction.

 

[Retrovert]

Should I replace the large canister capacitor as well or do they usually fair ok?

REPLACE.

Every electrolytic capacitor, particularly for power supply filtering, has either already failed or will immediately fail upon power up. Every electrolytic capacitor must be replaced. Such capacitors do not well age, and deteriorate in storage. These capacitors were not very good when new. Plus age and heat destroy electrolytics. Compared to today's inexpensive replacements they are junk which should be discarded. No magickal mojo exists.

The dielectric in an electrolytic capacitor, being oxides of aluminum, is a fragile creation, and it tends to re-dissolve back into the electrolyte if not used. While it may be temporarily reformed by gradually increasing the voltage, as was done when the dielectric was originally built, this creates a time bomb. The electrolyte, which was not particularly good chemistry at the time, has deteriorated.

If the filter capacitor shorts your rectifier cathode will be damaged or destroyed, the rectifier tube may (and probably will) arc, destroying the power transformer secondary. By the time the mains fuse (of sufficient current to handle the low-current B+ and the high-current heaters) blows, you've got slag for a power supply.

Many excellent guides exist on AK and elsewhere for restuffing the capacitor to preserve the original appearance.

 

[Derek G]

REPLACE.

Every electrolytic capacitor, particularly for power supply filtering, has either already failed or will immediately fail upon power up. Every electrolytic capacitor must be replaced. Such capacitors do not well age, and deteriorate in storage. These capacitors were not very good when new. Plus age and heat destroy electrolytics. Compared to today's inexpensive replacements they are junk which should be discarded. No magickal mojo exists.

The dielectric in an electrolytic capacitor, being oxides of aluminum, is a fragile creation, and it tends to re-dissolve back into the electrolyte if not used. While it may be temporarily reformed by gradually increasing the voltage, as was done when the dielectric was originally built, this creates a time bomb. The electrolyte, which was not particularly good chemistry at the time, has deteriorated.

If the filter capacitor shorts your rectifier cathode will be damaged or destroyed, the rectifier tube may (and probably will) arc, destroying the power transformer secondary. By the time the mains fuse (of sufficient current to handle the low-current B+ and the high-current heaters) blows, you've got slag for a power supply.

Many excellent guides exist on AK and elsewhere for restuffing the capacitor to preserve the original appearance.

Very much...Thanks!

 

[Derek G]

I have a couple of the smaller amps like yours that use 6V6's for the output tubes. One is an old Pilot and the other is a National Kit. The Pilot is a nice sounding amp due to the large output transformer and the National Kit is an okay performer. I buy my caps from Antique Electronic Supply, Just Radios and Mouser. I haven't bought into the theory that the boutique caps are necessary in old amplifiers as I can't justify the price for what is supposedly gained by using them. Even the yellow mylar caps that are very inexpensive will do a good job in your amp along with either carbon film or metal film resistors which are also inexpensive. There is no need in my opinion to try to source NOS carbon comp resistors for most restorations.

Thank you! Yes, I get most of my parts from Mouser. I just finished an order for a full resto on a friends 2230. Added the caps for this LJ-2 to it....

 

[Derek G]

View attachment 1385799 View attachment 1385789 View attachment 1385790 View attachment 1385791 Hello,

I'm newer to these forums. Thank God for AK. I've spent the past six months diagnosing and restoring a few Marantz units. I've learned quite a bit about solid state with much help. So. Here I am. Seeking more input. I have no knowledge in Tube Audio. But I'm very curious. Everybody has to start somewhere right? Today was a good day. I acquired a mono Realist (Radio Shack Boston) amp. Cleaning out a garage. It was given to me. Unbeknownst of any working condition. I couldn't wait to come home and investigate. This lil guy cleaned up really well. I hooked it up to my dim bulb and she appears good. All the tubes fire. Anyways. I googled it up. Finding its a LJ-5. Originally a Grommes LJ-5 rebranded by the Shack. Correct me if I'm wrong. I realize this is a single mono unit and to acquire "stereo" I will need a twin. So. How do I move forward? I wouldn't mind using this amp to listen to am "mono" channels with a single speaker hooked up to a time similer speaker. How do I test this amp? Can I use one channel from a pre amp output on a receiver? Also. How do I wire a speaker to it? It has four posts. C/4/8/16. I'm assuming 4/8/16 are ohms. What is C? Do I need a speaker with 1 wire? Any help would be very appreciated. See pics. I would love to hear this thing sing. Also. Everything looks great inside but.... Do I need to recap or replace anything moving forward. Thanks in advance. View attachment 1385788View attachment 1385789 View attachment 1385790View attachment 1385791

Edit: Btw after more research I've discovered it's actually a 1954 Grommes LJ-2. Branded by Radio Shack.

Kind of a cool read:

http://www.antiqueradio.com/Feb07_RadioShack_Tesla.html

 

[Tom Bavis]

I should have noticed the difference in tubes between the LJ-2 and LJ-5 - email for a copy of the Sams folder for the LJ-2: tbavis(at)rochester(dot)rr(dot)com

 

[primosounds]

Edit: Btw after more research I've discovered it's actually a 1954 Grommes LJ-2. Branded by Radio Shack.

Kind of a cool read:

http://www.antiqueradio.com/Feb07_RadioShack_Tesla.html

The Grommes LJ2 is quite often for sale on the bay and elsewhere. It is probably going to be more expensive than what you got yours for.