Where can I get a 5AR4 for my Scott

Jim Eck

Chicks dig the Mule
Well she made it a week. Now she won't play. I was hooking her up to my RSL monitors today to see how they would sound with her. Well... All of the tubes heat up but th 5AR4 Rectifier tube. I get no lights on the front of the Amp now either as well as no sound. I am probably wrong but I am going to assume that I hurt this tube putting the cover back on. It is a tight fit and I had this tube stretched out of the socket. Sound reasonable? Is there a tube brand preference for this application? Or have I got other problems?

Thanks, Jim:cry:
 
You might have had a fat bottle where a small one should go. If the insides turned white you sprang a leak and lost vacuum. Without the cage on you could pop a 5U4 in there as it will take the voltage and are common for rectifiers. Other than that there are a number of tube dealers on the net and 5AR4s are not cheap. The most sought after and therefore command some pretty good prices are Mullards. Yes the do sound better, but the GEs and RCAs are good and don't command the price.
Running tube gear, particularly amps, without the cages on is pretty much SOP because of the heat. If there are no little fingers to grab a hot tube leave the cage off.
 
5AR4 is kind of a unique tube, best to stick with it. Don't hurt your wallet looking for some NOS Mullard. The Sovtek and JJ's work well in Scotts. Don't go with a 5U4, it draws 3 amps fillament current. A 5AR4 draws 1.9 amps. In a pinch a 5Y3 will work but it doesn't have a cathode and the fast turn on will shorten the life of your output tubes. Also the high filter values will do in the 5Y3 eventually. The neon power light is connected to the B+ so if it doesn't light the B+ is missing.

Paul
 
Thanks, I hope this is it.

I have a tube coming from radiotubesupply.com I don't know for sure if this is the problem or not. The tube has not turned white. However everything prior seems to be heating up with this tube staying cold and no lights of the christmas tree. This all worked prior to me putting the cover back on and bending that tube over, so it seems like a good start to me. I am open to any suggestions however I am not a technician by any stretch of the imagination. I am just am user, enjoyer. There is one other tube that seems dim in brightness it is one of the 2 6BL8 tubes, it is not original Scott as the other one is. It is on the left side when facing the amp.

I'm not sure what is meant by B+. Is there something else I should be looking for?

I have not yet closed on the 5AR4 so if I need to add another tube now is the time to do it for shipping reasons.

Thanks, Jim
 
I would think that you tried to reseat the 5AR4. So if the tube is cold and doesn't glow you broke the tube or socket. The heater supply on the 5AR4 is seperate from the rest of the amp because of the high voltage on it. The B+ is the high voltage supply. It comes from the early days of radio when you had several batteries. A batt, B batt, C batt, ect. You will have three voltages in your amp. 6.3volts ac for the heaters of the output tubes and 6BL8 phase splitters, about 50 volts DC for the preamp tubes heaters run in series and negative bias supply and 440 volts dc for the B+ supply to the tube plates. The 5 volts for the 5AR4 doesn't count because it's part of the high voltage supply. The "ON" light is a neon lamp hooked up to the high voltage supply through a resistor, when you loose the high voltage (B+) it won't light. Kind of self diagnostic. I always preferred that scheme vs hooking a lamp to the switch or heater supply. But many people would disagree, especiially to the use of a neon lamp.

Don't worry about the 6BL8 brightness, especially if there from different manufactures. They are working, just differend design or manufacturing process. You may even see a different heater brightness in the same manufacturer tube.

Paul
 
Yes, I tried reseating it, and yes it was quite cold. I even left it on for a while longer than normal for it to warm up. If I understand what you are saying then it is probably either this tube or the socket that is the problem? And after replacing the tube if that is not the problem then a socket would be the next check. Is there a visual inspection that can be done of the socket? No cracks are noticeable from the top. Maybe stupid question but, would a burst of contact cleaner hurt to see if maybe just bad contact?

Jim
 
More clues?

One of the 7189 tubes is getting hot but is not glowing at all, should this tube be replaced while I am ordering tubes? It is an original Scott tube.

Jim
 
No more rectifier freebe's

I mean I only have two 5ar4s; a 1956 Amperex metal-base and a 1961 Mullard fat base and I'm keeping both! :D MikE
 
7189

It is not good. It came apart in my hand when I tried to remove it. Radiotubesupply is showing 7189A. Is this a tube that can be used to replace the 7189? I don't know the manufacturer or anything of that nature. I will inquire of them, I am currently waiting to hear about the rectifier from them.

But back to my question, is the 7189A a good replacement or should I look some more?

Jim
 
7189 = 7189a

7189A has screen connections on pins 6 & 9, whereas the EL84 and 7189 only have screen connections on pin 9. This is a consideration if one wishes to replace 7189A with EL84 or 7189, one might have to move screen connections to pin 9. A 7189 can always be substituted for an EL84. The other way around is a "NO-NO". The 7189 is rated for higher B+ voltage than the EL84. Regarding the 7189 and EL84, there are no electrical or physical difference between them.

MikE
 
If I understand

I should continue looking for 7189's instead of replacing them with 7189A. Does anyone have a recommendation for where to purchase these? Which are acceptable? Should I replace them all to keep them matched?

Thanks, Jim
 
How Many

... does that amp use? Those puppies are pretty expensive, least the vintage varieties from Ebay or tube boutiques. Unless you want to get into some tube rolling I'd just replace the one 7189 and then go from there. My buddie's amp uses EL84s, if you like I can ask him where he gets his stash. He may even have some to sell. And he only buys the very best stock. MikE
 
Careful with those 7189's in a Scott. They used one of the unused socket pins (pin 6?) for a circuit tie point. I don't think the Russian A versions tie G2 to pin 6. A 7320 should be OK. A 7189A may send the amp up in smoke. I've had it happen. Best to use matched tubes but you can try to get a close match in circuit when doing the bias adjustment after replacing a single tube . Depends how much you are willing to spend and how much you are going to use it. Search the archives at www.hhscott.com for info on these units. I've had several of these amps. I think the 7189 amps are a little bright compared to the 7591 but they can sound really good on the right speakers as long as you don't expect a lot of volume and bass. They are only about 25WPC. Unfortunately now it sounds like the time to get a schematic and poke around. But if you're uncomfortable doing it I wouldn't recommend it.

Paul
 
I have the original manual and schematic, got it with the amp. I have ran accross these do you have any experience with these. I have been told that the EL84M may be a good replacement. Since this is a different tube so to say, would it be better to get the matched quad. Is there anything I should know about these tubes in particular. Any experience?

Jim
 
Re: 7189 = 7189a

Originally posted by MikE
7189A has screen connections on pins 6 & 9, whereas the EL84 and 7189 only have screen connections on pin 9. This is a consideration if one wishes to replace 7189A with EL84 or 7189, one might have to move screen connections to pin 9. A 7189 can always be substituted for an EL84. The other way around is a "NO-NO". The 7189 is rated for higher B+ voltage than the EL84. Regarding the 7189 and EL84, there are no electrical or physical difference between them.

MikE

EXCUSE ME... but I kinda think that is All Wrong... now most tube experts think they know it all, but well, this is a technology from when when our parents were young, and all of the nuances might not be readily apparent 40 or 50 years later.. so here goes !~~!

First of all. as far as I know 6BQ5, 8BQ5, 10BQ5, and EL84, 7189, with pinout as type 9CV and the 7189A as pinout 9LE are all pretty much interchangeable, and perhaps are functionally identical. Its also possible that the "higher voltage" rated tubes were just tested to a higher voltage level, but are not actually mechanically or electrically different ( a statement which maybe conflicts with some of what is quoted above ).

Now I'm not stating for sure that all six tube types are identical, there could be true differences between 6BQ5 / 7189 / 7189A, but this possibility has never come up in any prior discussion that I can recall.

IF one looks carefully, among the RCA and Sylvania and other tube manuals from ancient days, one sees that these books show pin #6 on the various six tubes mentioned above, either as G2 or IC. Now to me, IC means "Internal Connection" which could be considered a bit ambiguous. I'm afraid that "IC" might mean pin 6 is connected to a shield, or G2, or basically anything they wanted to connect it to, even nothing! So does it also mean the same thing as connected to G2 - but is just denoted differently by RCA on the 6BQ5, EL84, and 7189 as compared to Sylvania on the 7189A which shows pin 6 connected to G2 ? Well, I don't know. There are different pinouts 9CV and 9LE which does show a difference on pin 6.

So - has anyone taken a whole bunch of these aforementioned vintage and modern tubes and run meter tests between pin 6 and pin 9 ( and perhaps pin 6 and the others ) to get the true lowdown ???

I'm sure gonna pull some tubes from boxes and run some tests this weekend...

-Steve
:smsex:
 
Funny you ask

When did I become an expert? Thank you for the promotion from dufus. I've never claimed any particular knowledge in that field. The information provided was from a good source but I won't swear to it. Speaking of experts, here's a link to a recent thread on the [7189/7189a] subject.

http://www.audioasylum.com/scripts/...=tubes&m=122574 MikE [Tube Expert Wanna-Be]


BTW - I'm not familiar with your moniker - Welcome to AK!
 
I checked a lot of tubes tonight...

And here is what I found...

While the Tube Manuals say that on 6BQ5, 8BQ5, 10BQ5, EL84's, and 7189's pins 1, 6, and 8 are "IC" - that varied!

On most tubes Pin 1 was internally connected to pin 2 {G1}, except for the Russian 6BQ5/EL84, its pins 1 & 2 were the only ones NOT CONNECTED. This was also seen in one Browning "Made in England" tube which I'm now 100% sure was Russian made.

I didn't have any Russian made 7189 or 7189A tubes so I can't say anything about them.

On all tubes except the 7189A's pin 6 was NC. and pin 8 was NC. On 7189A's Pin 6 is connected to Pin 9 and pin 8 is NC. 6BQ5's ( at least the GE's ) appear indentical to 7189's when comparing within the same brand.

The amount of variations was totally unbelieveable between brands, some had pins 6 and 8 cut off, others had 1, 6, 8 close to other connected pins, while in some pins 6 and/or 8 were touching the lower mica insulator, possibly holding the assembly in place.

Russian tubes had pin 1 physically soldered in place to a rivet mounted in the lower mica holding it in place. I'm sure these physical differences translate into performance differences.

Despite what some tubes were labelled, looking at several dozen, it was easy to spot the RCA made ones from the Westinghouse, from the GE, from the Sylvania's, from the Russian made ones - regardless of the brand printed on the tube.

So yeah, use caution - don't use the 7189A's unless the circuit specifically calls for its use, and do check the schematics and chassis to see if tube pins 1, 6 and 8 are used as tie points.

What a MESS!

-Steve
 
Back
Top Bottom