R2700A receive low

[twister526]

The receive on my R2700A seems weak, first one I have owned, the only thing I can compare to is my newer radios. If I receive someone say 3 on singnal plenty of audio on my Galaxy 95T , I receive hardly any signal and very weak audio on the browning. I basicly have to run pre-amp to talk to my buddies 30 miles away, that I normally hear fine with no pre-amp. Just looking for a little direcection, or input. Thanks

[2600]

It doesn't just "seem" weak, it IS weak.

A pretty common problem with a 44 year-old radio.

But what I'm reading between the lines may be an even bigger problem.

You wouldn't buy a 1965 car and hope that the right "tune-up tip" will restore lost compression, get it to stop burning oil, fix the leaks around every seal, gasket and hose, and all that other stuff. If the mileage is low, that would be good. But getting it back on the road will look a lot more like "restore" than "repair".

Browning receivers from before about 1968 will tend to be very expensive to restore. Three hundred bucks or MORE is not unusual. And that's JUST for the receiver.

I could bore you with technical details, but for now I think this is probably enough bad news.

Or maybe more than enough.

And if you're in love with the idea of using this receiver, that's okay too. Just remember. True love is never cheap.

73

[BionicChicken]

Before you freak out on a $300 overhaul first you can check a few things. Have you tested the tubes? 1 weak tube can cause your problems. Granted there may be more things wrong but a radio that is "44" years old most likely has had some sort of repair done to it through the years so hopefully not everything in it is bad. Tubes and capacitors are the first things to check along with cleaning dirty controls.
Has the radio set up for a long time without any use? Did it just all of a sudden start to have a bad receiver? Do stations that are close to you give a good signal and audio or are all of them low? Rather than just taking for granted that it needs a complete overhaul checking a few things can shed light on where the problems may be......................there is a chance they could not be major.................not a big one............but a chance worth taking.

BC

[mark4]

Most of the time when a radio like this goes south.
Many owners try replacing tubes. It's the easiest thing to do.
So you may get a few newer ones in it. Maybe?
Or 1 or 2 capacitors. But it will still need a major overhaul.
Everyone I have worked on that has had some repair work needed to be done over again anyway. Didn't really make it cheaper. Usually there are much bigger fish to fry. And still a laundry list of items that need to be replaced. If you really plan on USING it.

[BionicChicken]

Sept 25, 2009 17:31:42 GMT -5 mark4 said:

Most of the time when a radio like this goes south.
Many owners try replacing tubes. It's the easiest thing to do.
So you may get a few newer ones in it. Maybe?
Or 1 or 2 capacitors. But it will still need a major overhaul.
Everyone I have worked on that has had some repair work needed to be done over again anyway. Didn't really make it cheaper. Usually there are much bigger fish to fry. And still a laundry list of items that need to be replaced. If you really plan on USING it.

If the radio works............half the battle. If it has worked for a while......................more than half. Don't put someone down for having a radio that doesn't receive as good as it should because it is many years old. Maybe it just happened. I know I am stepping out on a limb but don't discourage someone right off the bat with his radio needs many hundreds of dollars worth of work. Maybe it does...........maybe it don't. No other details have been provided except it didn't hear well. Many things can cause this.
I just hate to see someone with a good radio get sidetracked because someone told him it was bad without even seeing the radio. No one is a physic. Yes....most probably it needs work. But what if this particular radio has already been worked on by some of the self proclaimed "gurus"? What then?

[2600]

Mr Twister,
I hope we haven't ticked you off or scared you away.

But here's the question:

Will this radio prove to be a "fixer upper", that has only a few small problems?

Or will what it really needs prove to be a "100,000-mile tuneup"?

The advice above is good, especially concerning the tubes. They are a wild card. They may all be good.

They may all be bad.

Odds are that more than one is bad. The important thing to know is which ones.

And if you read any book from that era on the subject of electronic repair, the author will present you with a statistical fact. The most likely component to fail is a vacuum tube. The second-most likely kind of component to fail is an electrolytic capacitor.

Even if you get it running with 44 year-old electrolytic caps still in it, they seldom last for long, once the stresses of operating catch up with them. The reason for the advice to "re-cap" an old radio is to prevent predictable breakdowns, once the radio becomes functional again. The factory caps will fall like dominoes, one by one until all of them are replaced. Doing it all at once saves on labor. And prevents collateral damage that can occur if one of them fails as a short to ground.

Can you read a schematic? This is an unfair advantage any time a soldered-in component fails. Those can be hard to troubleshoot unless you can read the "road map".

But seriously, a tube tester is the first tool you need to track down. Simply replacing tubes at random is like shooting in the dark. You may hit something, but if you do, it will be by accident. And if there are three different problems keeping the receiver silent, fixing only one or two of them still leaves you with a receiver that doesn't work.

Too bad the radio doesn't have an odometer. Could be helpful to know if it's on the first or the second 100,000 miles.

73

[mark4]

1st off. I don't see anything that anyone has said on here as putting someone down, at all! Everyone here, that I see is trying to help out other people with their radio issues. Not a good idea to read into someones words. And accuse of putting someone down. If you disagree with someones technical advise, You simply disagree.

[twister526]

I would like to start out by saying I appreciate all help and advice. The way I look at it is if you respond and take the time to reply you must care, and are trying to help in some way, so thanks. I guess I wasnt very clear with my initial post and thats my fault. The radio in my opinion is in really good condition inside and out, but most importantly inside. Very clean and I dont just mean dirt free, I also meen not been hacked on, and any repairs over the years and i am sure there has been some, are not noticible, which is a good thing, to me anyway. The thing does receive, just not as strong as I feel it is capable of, even being an older radio, I have other tube radios just as old that receive better. I am capable of reading a schematic, I do my own work always have, I am capable of rebuilding this thing myself , just looking for people with diffirent ideas and opinions and thats what im getting, and thats great! I realize there are alot of you out their alot better educated and familiar with the tube radios, and brownings. Just looking to learn more from you all and maybe I can be of help to someone someday about the receive on an R-2700A, thats what it is all about, and I do want to operate my radio at full capacity as well, and will with all the help. Thanks again!

[BionicChicken]

Not reading anything into any statements made. Just when someone right off the bat answers a question without knowing anything about the radio (except the receive is low) and tells them to be ready to spend a huge amount of money on it..........that stinks. Many radios have been thrown into closets and worse by such advice.

Now then, the fellow comes along and has technical ability (or so he says) and really just wanted someones opinion on what could be wrong. All too often people hear what kind of radio someone has and start preaching about it needing a 100,000 or 200, 000 mile tuneup without knowing anything about it..........just because it has age on it. Who knows, maybe someone has done a 100K tuneup to it already? Components fail regardless of age and who worked on it.

To me telling someone their equipment is going to cost large sums of money without having examined it is a put down, if nothing else but on their intelligence. You can never judge the knowledge that someone has by one of their posts. Maybe someone might be making a post just to test how smart some of the folks on here are.

[mark4]

I stand behind what In said earlier. And from the response I see people appreciate the advise they get out here. Whoever is recommending a 100,000 200,000 tune up or whatever. The best advise I got when I started out repairing old tube radios was to change out every last electrolytic capacitor. My thoughts are when you order them all at one time it sure does save a heck of allot of money on shipping! And if you have the know how to do it yourself it won't cost you a arm and a leg.

[**GRUMPY**]

Oh brother I come back from being away for a while and I come back to this? Come on guys, grow the hell up a little!

Twister, since you already own other tube radios I'm sure you are aware that most won't receive as well as your 95T will. I would start with checking for any weak tubes since that would be your easiest fix. If that doesn't work then check the caps and go from there. All three of the guys that have answered your questions are pretty smart guys who have been around radios for years. Not sure what happened here, but it needs to stop, NOW!!!

THERE IS NO ROOM FOR EGOS HERE!!!

Twister, I hope this doesn't scare you away from the forum. Most times things go smooth around here. Feel free to ask as many questions as you like!

Scott -aka- Grumpy

[2600]

Thanks for hanging in there, Twister.

Sounds as if you are set up quite well for this kind of work. You'll understand why I ask. Not everyone has both the tools and the experience to use them with success.

If you don't have the schematic, here is a link to a full-size scan

img233.imageshack.us/img233/4213/r2700a10.jpg

Let me know if it won't download at full-size resolution. A 'shrunk' copy won't be legible.

I would start with the screen-grid voltage at pin 6 of the two 6BA6 tubes V4 and V5. Should be within about 20% of the value shown on the diagram. If you compare this receiver to the later models, you will see a third 6BA6 IF-amplifier tube in all later models. This model does in fact have one less IF stage, and will never compare favorably to newer Browning receivers for weak-signal sensitivity. There is a reason Browning added that third 6BA6 IF tube in their later-model receivers. The added signal gain from a third IF-amplifier tube makes a difference to the weakest signals.

But checking DC voltages on the plate of V4 and V5 is better done at the junction of either R54/C34 and R20/C31. This is the "cold" side of the IF-transformer on each tube, and touching the probe there won't disrupt the circuit the way probing a tube's anode (pin 5) will tend to do. If the plate and/or screen voltage on V4 or V5 is low, the resistors feeding these points get checked next.

But you should always be able to hear a rise in the noise level when the antenna attached. If you can't tell by listening whether or not the antenna is connected, (ANL off) this points to a receiver that's lacking sufficient sensitivity.

The single biggest cause for high-dollar pain in this radio has to do with a component called the "K-Tran". If you have a look at the adjusting hole in the top and bottom of T3, T4 and T5, you will see a wide screwdriver slot, rather than a hollow six-sided hole. This type of RF/IF transformer uses a cup-shaped ferrite tuning core that surrounds the winding that it tunes. This design provides magnetic shielding for the coils inside. The K-Tran was a high-tech, high-performance component in 1965, but they do not age gracefully. Inside the 455-kHz IF transformers you will find two capacitors. In the later-type 'hollow slug" IF transformers, this is a ceramic-disc or polystyrene/foil capacitor, one wired in parallel with each winding inside.

The K-Tran uses a stack of metal plates and mica insulating sheets pressed against the inside of the plastic base. This type capacitor has a very low series resistance, and would be very temperature stable when it was new. The K-Tran was designed to provide tuned circuits with a very high "Q" factor, which serves to narrow the receiver's selectivity, and improve its rejection of the adjacent channels. The construction of those internal resonating capacitors is just part of that design. So far so good, but fast-forward to 2009.

The clear polystyrene frame inside the K-Tran has shrunk and begun to show tiny cracks called "crazing". Since the stacked-plate capacitors in the base are held together by a spring riveted to the hole in the bottom of the K-Tran, any shrinkage of the plastic causes the tension of that spring to slack off. Causes these plates to shift around ever so slightly. That causes the capacitance to change, and the resonant frequency of that coil to drift away from 455 kHz where the slug was (we hope) tuned for max signal.

Once this happens, you have an IF transformer that either:
1) Won't tune for a peak, no matter where you turn the slug, or:
2) Causes the signal level to jump up and down with even the slightest touch of an alignment tool, usually on the hole for tuning the under-side slug.

Repairing a K-Tran may work for someone else, but drilling out the brass rivet to remove those internal capacitors usually ended badly for me.

Replacing them is not cheap. The "C-141" 455-kHz IF transformer used in later Browning radios works just fine as a replacement, but is not cheap. Hence the routine prediction of a high repair cost.

And the last 25 or more estimates prepared here for that model reveal a trend. Not a certainty, but strong odds that the receiver will have one or more bad K-tran IF or RF transformers. And once the receiver is returned to regular service, the remaining K-Tran parts will "remember" how old they are and start to fail one by one.

I can't tell much about a particular radio's condition without seeing it, but after the first 50 or 100 of any particular model, the patterns will emerge. If you're paying attention.

The odds of a "modest" repair cost for one of these really IS related to the mileage. The clear polystyrene inside a K-Tran will deteriorate from age alone. But the heat of operating the radio will speed up the process. A low-mileage radio may have NO bad K-tran parts in it. Not likely, but it MAY.

Or it may have several. The "high-mileage" radio is guaranteed to have more than one of them in bad shape.

Just be glad it's not the later "R27" model. That one has six of the 455 kHz IF transformers, rather than three. Never mind what a high-mileage restoration will cost for that model.

And when a radio slips past that 40-year mark, the line between "repair" and "restore" will begin to blur.

Best of luck and 73

[rjordan]

Hi Twister,

Well, if you're still hanging in here, I'll add a few more comments which might help out.

I dug out my notes, blew off the dust and found some things that might be helpful. Chances are pretty good that you have these old KTran transformers in your radio - my lab book has its first entry on coming across this problem on a Browning Mark II - and I wrote "and earlier" next to the entry. I also show notes about these transformers having 1655-2, or 119-XX-YY, where XX is year of manufacturing I THINK printed somewhere on them.

I also have notes where I came across early vintage RX units that had the "newer" C584" transformers in place of the older 1655-2 units. The installation look "fresh" from the factory. When I talked with Phil Nichols about this problem back in the early 90's, he was just replacing defective transformers - at that time he had a ton of the newer versions in stock, and was only charging $10.00 each for them, so replacement back then was cheaper than the labor to "fix" the transformer.

The KTran transformers that Nomad refers to usually display one of two (perhaps both) symptoms when they fail.

The first symptom is low RX sensitivity. The second is random "popping" or static sounds in the RX. Either or both is an indication that the mica plates at the bottom of the transformer have problems. The transformer's "Q" can drop to practically nothing with the contaminated plates. I used my Boonton 260 Q meter years ago to track down the problem and verify exactly what was going on.

Here's a great link to give you some idea (complete with pictures) of what we're talking about here. www.radiomuseum.org/forum/if_transformer_repair.html

If you look at the top of your 455kHz transformers, you'll see KTran printed on the top of the aluminum can, and they'll be two small pieces of plastic protruding through two squarish holes as I remember.

I had no problem fixing them - at last count well over 100 were in my log as having been repaired. I got to the point where I just used a very small nosed, sharp pair of wire cutters to split the brass rivet in about 3 or 4 places, and then a fine pair of needle nose to gently remove the rivet. The link I pasted above gives you the rest of the story - pretty much the way I was doing it 15 years ago.

Now, as Nomad says, if you have one bad, then you need to fix them all.

The newer transformers not only used individual caps internal to the transformer (as opposed to the "plates"), they also used Litz wire, so there was an increase in the "Q" from that change as well.

If you need to repair the transformers, be sure to make a good drawing (pictures are even better) of how the transformer is mounted and hooked up (look for a "dot" or drop of paint next to one of the 4 pins on the bottom of the transformer. Mark the chassis next to where this dot is located, and put the transformer back in the same physical location). Wiring layout is critical, and you want the wiring to go back as close to the places as it came out - you don't want your amplifier to become an oscillator.

The only problem you might have is how to check each transformer after you've rebuilt it. If you're familiar with troubleshooting by signal injection, then start by rebuilding T5, injecting a signal into the grid of V5, peaking your "rebuilt" transformer, then moving to T4, etc. If this is not something you're familiar with, now's a great time to learn.

Get on Alibris.com or Amazon and buy yourself a copy of Practical Radio Servicing by Marcus and Levy - get the 2nd edition (copyright 1956 and 1963). Right now there's one on Amazon for $15.00, and there's also one on Ebay for $2.00 bid, or buy it now for $10.00

While the book is primarily geared towards broadcast and shortwave band receivers, I think I learned more about actually REPAIRING tube radios from reading that book as a teenager than I did from 6 years of Electrical Engineering classes.

The first edition is good if you can find it, but MUCH more expensive, as it's become a collectable, and it deals with the older series of tubes (octal/loctal versus miniature tubes)


Let us know if you have any questions. Hopefully, you'll just find a weak tube or two.

Oh, and if you attempt an alignment and find some of those IF transformers will not show any "peak" when you adjust them, you've pretty much verified they are bad - the Q is so low on a bad transformer that you cannot peak them at the IF frequency.

Even if you have some bad transformers, you'll only looking at a few hours labor, and about 5 or 6 dollars for a handful 330pf Silver Mica capacitors. Sure beats having a hobby restoring Corvettes !!!!

And I can already see the SMILE that will come on your face once YOU fixed YOUR radio....

Good luck,

Rick

[Sandbagger]

Sept 28, 2009 15:14:19 GMT -5 rjordan said:

Hi Twister,

Well, if you're still hanging in here, I'll add a few more comments which might help out..........

Good luck,

Rick

That was a wonderful piece of information. Thanks for posting it!

[twister526]

Thanks again guys for all the info, advice, help,opinions, everything, and I do meen everyone, and everything. Your a great bunch of guys, and this is a great forum, just glad to be a part. As for the radio, I am gaining on it every night, I have replaced the capacitors, this has made quite an improvment. I have gained about two numbers on receive, the tunning is much more responsive now. My next plan is to order some new tubes, I just replaced caps because I allready had them. I realize that there maybe alot more to come with transformers and all, but with the knowledge I have allready gained from you all I am feeling pretty good about the whole thing. Thanks again to all! Twister526

[rjordan]

Way to go! There is nothing wrong with taking it a step at a time. The most important thing is to have fun.

You mentioned you had changed all of the caps. Just want to mention that sometimes C57 is easy to overlook - it's a 4uf electrolytic cap tied between V8 (the 6AQ5) pin 2 and ground. If this cap opens, then you're receive volume will be lower than normal, as it provides AC bypass around R38 to audio frequencies. If it shorts, then V8 is going to run hot, as R38 is used to provide "self bias" to V8. I've seen that cap go both ways - sometimes open, sometimes shorted, as it really gets cooked sitting under the tube and right next to R38.

If you've changed it, ignore all of this, but if per chance you missed it, I'd highly recommend putting a new one in it's place ASAP, watching polarity during installation. While your in that area, check the resistance of R38 - it's supposed to be 270 ohms. It's high on the list of resistors that get "cooked" LOL! If the color bands look pastel in color, (or even worse), I'd replace it with a new one. Modern 2 watt resistors are just about the same size as that old 270 ohm 1 watt resistor, and can usually be found at the local electronics parts house - or ordered from the likes of Mouser or Digikey, etc.

You're making me want to dig in the attic and pull out a couple of old sets that need fixed up. We have vey little activity here these days, so even if you get a radio working, there's no to "ping" to

Keep us in the loop on how things are going!

Rick

[rjordan]

Twister, if you do end up changing out R38, even though I mentioned a modern 2 watt is about the same size, I would try and find a 1 watt replacement (which was the original rating of that resistor). That resistor under normal conditions is only dissipating around 0.37 watts. While its purpose it not to act as a fuse, if V8 ever shorted, you would hope you could burn R38 open before the primary windings of T6 failed due to excessive current. A 1 watt resistor should "give up the ghost" faster than a 2 watt resistor. I'm not certain in a shorted V8 condition what would go first given the age of some of the components and their condition, but in this case, the original rating would probably be the best choice.

Take care, Rick