Silvertone 1484 output transformer taps

[Intergalactic Tourister]

The 1484 schematic does not say what the opt secondaries are...

On a different forum, Bruce from Mission Amps believes the unused tap is 2 ohm.

On Vintage Amps forum, Johnny Savant says the unused tap is 8 ohm.

Soundmasterg, on this forum, says it's 2.6 ohm.

Does anyone know for sure? I do know the yellow wire is factory wired for a 4ohm speaker load. The red wire is a mystery.

[loudthud]

I always thought that the 1484 and 1485 used the same OT, the 1485 just had two of them. So 2.6 ohms would make sense for a 1485 because that amp had six 10 inch speakers, two banks of 3 each 8 ohm speakers wired in parallel.

[Intergalactic Tourister]

Just looked at the 1485 schematic... seems to make sense. Thanks.

So, each 1485 OPT must be factory wired using the red wire tap (2.6 ohms) for three 8 ohm speakers wired in parallel.

I just hope the 1484 & 1485 OPTs are the same internally.

[soundmasterg]

Just looked at the 1485 schematic... seems to make sense. Thanks.

So, each 1485 OPT must be factory wired using the red wire tap (2.6 ohms) for three 8 ohm speakers wired in parallel.

I just hope the 1484 & 1485 OPTs are the same internally.

They are the same exact transformer. The yellow wire is 4 ohms and the red is 2.6 ohms. I verified it with some testing when I worked on my brother's amp years ago.

Think about it from a business perspective....why make two transformers for two amps when you can just make one and use it on both? They were super undersized anyway. The stock 1484 is about 25 watts RMS...my brother's is 30 watts because of some changes I made to it, but that is about all you can get out of that OT with the tube complement and voltages. Take a look at a Fender with the same tube complement and voltages and you are around 55 watts for a Super Reverb with today's wall voltages. Only real difference is the OT and the phase inverter. The key thing to remember with the 1485 is that if you only want to use half of it, you need to remove two of the power tubes or run the unused half through a dummy load while you use the other half. The stock OT often blow on these amps due to being so undersized and due to people not understanding that you need to run a load on the unused half in the 1485 or pull the tubes on the unused half.

Greg

[Intergalactic Tourister]

Think about it from a business perspective....why make two transformers for two amps when you can just make one and use it on both?

That was precisely my justification for my assumption. However, amp makers have been known to change parts or manufacturers for a given amp model. So one amp model could have different parts. Plus I've never actually seen the 1485 OPTs. And there's no info on the schematic.

Plus when I make assumptions and feel like I can't possibly be wrong, something would blow up shortly after.

But thanks for the much appreciated info... I was going run a 1484 head through an 8 ohm cab from what I now know to be the 2.6 ohm output.

So if the 1484 were to run at half power (one 6L6 removed) then you should plug an 8ohm cab into the 4-ohm tap. In other words, you've effectively changed the OPTs 4-ohm tap to an 8-ohm tap... and the 2.6-ohm tap to a 5.2-ohm tap by removing one 6L6.

[soundmasterg]

That was precisely my justification for my assumption. However, amp makers have been known to change parts or manufacturers for a given amp model. So one amp model could have different parts. Plus I've never actually seen the 1485 OPTs. And there's no info on the schematic.

Plus when I make assumptions and feel like I can't possibly be wrong, something would blow up shortly after.

But thanks for the much appreciated info... I was going run a 1484 head through an 8 ohm cab from what I now know to be the 2.6 ohm output.

So if the 1484 were to run at half power (one 6L6 removed) then you should plug an 8ohm cab into the 4-ohm tap. In other words, you've effectively changed the OPTs 4-ohm tap to an 8-ohm tap... and the 2.6-ohm tap to a 5.2-ohm tap by removing one 6L6.

Let me clarify a couple things as I wasn't clear enough in my previous post.

The 1484 has a single OT with two power tubes. The 1485 has four power tubes with each pair using their own OT, so a total of two OT's in the 1485. If you only want to use one speaker cabinet for the 1485 and don't have the original cab that is 2.6 ohms per side, then you have a problem because you will mismatch unless you rewire to use the 4 ohm tap. A partial solution is to pull two power tubes and only run one half of the amp, and then the side that is not being used isn't going to self destruct. The other part of the solution with a 1485 is to rewire so you can use the 4 ohm tap or make a cabinet with 3 eight ohm speakers wired in parallel in it. A lot of these OT's have blown up over the years because people using 1485's will only plug in one OT but leave the power tubes working away for the other pair. Signal is still going into the other pair but has nowhere to go out so eventually the OT blows. Pull a tube pair and then you have something that will be ok.

The 1484 is different in that it only has two power tubes. The amp is push-pull so if you pull one power tube, it isn't designed to be single ended so won't sound all that good and will hum a lot. Best to run that amp with both power tubes in at all times. If you want to run it into an 8 ohm cab off the 4 ohm tap, it will work. My brother ran his for years that way before I modded it, and it worked fine. Yours should also, but don't hold me to that....these are very undersized OT's! The sound changes though....becoming a lot more compressed....the bandwidth narrows...it distorts a lot more...volume goes down. It will work but a 4 ohm load on the 4 ohm tap is better. If you are determined to use an 8 ohm load and you don't want to deal with the downfalls...then you want to get a Weber replacement OT which has a 4 ohm and an 8 ohm tap. Other than that difference they are supposed to be the same.

Hope that makes things clearer.

Greg

[Intergalactic Tourister]

The 1484 is different in that it only has two power tubes. The amp is push-pull so if you pull one power tube, it isn't designed to be single ended so won't sound all that good and will hum a lot. Best to run that amp with both power tubes in at all times.

Greg

I thought you were very clear.

But I actually found that out by accident. One day I put one 6L6 in the 1484... got distracted... then a day later decided to play the amp. I didn't really notice any difference until I turned up pretty loud. I started checking my cord, guitar, then looked in the back of the amp and saw only one 6L6 in there!
But I didn't think it sounded bad at all. In fact I couldn't really tell the difference at a small room type volume.

But then I thought with one 6L6 pulled out the 4 ohm tap becomes an 8 ohm tap... and I was playing through the 4 ohm cab at the time. I figure now I can use only one 6L6 and play it through the 8 ohm cab this way.

But why does it still sound good with only one 6L6 if its push/pull?

[boroman]

Let me clarify a couple things as I wasn't clear enough in my previous post.

The 1484 has a single OT with two power tubes. The 1485 has four power tubes with each pair using their own OT, so a total of two OT's in the 1485. If you only want to use one speaker cabinet for the 1485 and don't have the original cab that is 2.6 ohms per side, then you have a problem because you will mismatch unless you rewire to use the 4 ohm tap. A partial solution is to pull two power tubes and only run one half of the amp, and then the side that is not being used isn't going to self destruct. The other part of the solution with a 1485 is to rewire so you can use the 4 ohm tap or make a cabinet with 3 eight ohm speakers wired in parallel in it. A lot of these OT's have blown up over the years because people using 1485's will only plug in one OT but leave the power tubes working away for the other pair. Signal is still going into the other pair but has nowhere to go out so eventually the OT blows. Pull a tube pair and then you have something that will be ok.

The 1484 is different in that it only has two power tubes. The amp is push-pull so if you pull one power tube, it isn't designed to be single ended so won't sound all that good and will hum a lot. Best to run that amp with both power tubes in at all times. If you want to run it into an 8 ohm cab off the 4 ohm tap, it will work. My brother ran his for years that way before I modded it, and it worked fine. Yours should also, but don't hold me to that....these are very undersized OT's! The sound changes though....becoming a lot more compressed....the bandwidth narrows...it distorts a lot more...volume goes down. It will work but a 4 ohm load on the 4 ohm tap is better. If you are determined to use an 8 ohm load and you don't want to deal with the downfalls...then you want to get a Weber replacement OT which has a 4 ohm and an 8 ohm tap. Other than that difference they are supposed to be the same.

Hope that makes things clearer.

Greg

I have a question because found nothing about that on the web - 1485 has dual OT, each one has yellow wire and red-with-yellow wire (lets call it red, simply). The red ones are 2,6 ohm taps, the yellow ones are 4 ohm taps. In my case two red ones are joined together on the terminal and then it goes to the output jack. The seller claims that it's wired for 4ohms. Is it really? I think using yellow terminal joined would be 4ohm out, right? That's my 1st question. Second - I have nothing connected to the other pin of the output jack, do I need to connect black (ground) there?

Thanks