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**Gtr_tech** · 02-10-2009, 06:25 PM

The output transformer in those is *very* failure prone. I'd upgrade it with something beefier, but make sure to measure first 'cause the clearence to the top of the cab is tight. Yea, I'd recap it before powering up, and add a 3 wire pwr cord. I went through one a couple years back and changed the standby switch to a std arrangement, IE interrupt the B+. As it sits its a mute switch that shorts both sides of the signal after the PI, cancelling any output. I also changed the front end input stages from the shitty sounding grid leak bias to regular cathode bias type. Brought that thing right to life.

They're ok amps, but really overrated since the whole White Stripes thing.

**olddawg** · 02-10-2009, 07:40 PM

Originally posted by Gtr_tech View Post

The output transformer in those is *very* failure prone. I'd upgrade it with something beefier, but make sure to measure first 'cause the clearence to the top of the cab is tight. Yea, I'd recap it before powering up, and add a 3 wire pwr cord. I went through one a couple years back and changed the standby switch to a std arrangement, IE interrupt the B+. As it sits its a mute switch that shorts both sides of the signal after the PI, cancelling any output. I also changed the front end input stages from the shitty sounding grid leak bias to regular cathode bias type. Brought that thing right to life.

They're ok amps, but really overrated since the whole White Stripes thing.

Yeah, I was looking at the schematic and notice the wierd standby arrangement. I was going to ask about it because it didn't look like it was in the B+ line at all. BTW, do you have a link or directions on how to convert the grid leak bias to cathode bias in the front end. I assume you are talking about every stage before the PI and excluding the reverb driver/return.

**Gtr_tech** · 02-10-2009, 08:05 PM

The grid leak arrangement only applies to the first stage on each channel. The cathode is straight to gnd with a high value (several meg) R to gnd at the grid. I believe I just used the std Fender 1.5k/22u cathode circuit and added a 68k grid stopper at the grid. It really cleaned it up nice and got a more usable distortion when pushed.

**olddawg** · 02-10-2009, 08:12 PM

Originally posted by Gtr_tech View Post

The grid leak arrangement only applies to the first stage on each channel. The cathode is straight to gnd with a high value (several meg) R to gnd at the grid. I believe I just used the std Fender 1.5k/22u cathode circuit and added a 68k grid stopper at the grid. It really cleaned it up nice and got a more usable distortion when pushed.

OK, I understand this. Thanks a lot. Do you have a recommendation for a specific transformer? Also do you know if the amp covering (it isn't tolex) is available anywhere? Thanks again!

**tboy** · 02-10-2009, 10:26 PM

This schematic shows cathode bias on the input stage:

http://www.ampix.org/albums/userpics...ertone1484.jpg

Do you have a different schematic? If so I'd like to add it to ampix.

**Gtr_tech** · 02-11-2009, 02:03 AM

I don't remember exactly what I ended up putting in that.....it was just a stray laying around. I'd have a look at what alot of the "big box" mfgr's are using....IE they're pretty undersized for the application. The 50w Mesa recto I sent out the door a week or so ago had an output xfmr that would go into that amp. It was failed, and half the reason the amp was in for repair.....but it would fit. I think a 50w Mar$hall replacement will be too tall. Perhaps look in the Hammond xfmr catalog....one of thier "universal" replacements may fit the bill and the available real estate.

**Gtr_tech** · 02-11-2009, 02:08 AM

Lemme see if I can find it. I know I had to hunt around to find one that matched it.

**soundmasterg** · 02-11-2009, 07:43 AM

Yeah, every Silvertone 1484 and 1485 that I've ever seen had cathode bias on the first two stages, so maybe you're thinking of some other Silvertone model?

If it had water damage, there is a strong liklihood that all transformers are bad...I resurrected one that had water damage and the PT, OT, and choke were all bad. I found a cheap one that looked terrible on ebay and swapped the appropriate parts over to my excellent looking but non-functional one.

If you decide to use a larger OT, then you can modify the screen tap for the power tubes to get it's voltage off the actual B+ instead of one section down as it is now. Add a filter stage and dropping resistor off the B+ and you're good to go. The amp will put out a lot more power this way. Another suggestion would be to change the dropping resistors for the preamp stages to get the voltage higher.....they are around 90v and sound lousy down there and have low gain. Adjust up to 150v or better and you'll get more gain and a brighter and more harmonically rich sound. Be careful going too far however as the layout of the amp, and in particular, the location of the PT can cause severe hum problems with too much gain. If the reverb doesn't work, don't bother as it is one of the worst sounding ever put in an amp....on the other hand the tremelo is one of the nicest around when working correctly. Replace all the pots, coupling caps, and most of the resistors. Also replace the selenium rectifier diodes with some 1N4007's. Replace every electrolytic cap in the amp. Once you get done you'll have a great sounding amp, and you'll forever hate working on 1484's again...haha!

I've posted a LOT of info on these amps on the Hoffman board over the last couple years, so search the archives over there if you like for more info.

greg

**olddawg** · 02-11-2009, 08:04 AM

Thanks for the advice Greg. The speaker cab got wet a little. (It doesn't take much to mess up that ancestral particle board) The amp is clean and in good visual condition. Someone suggested that a Deluxe Reverb replacement OT works well with these amps? I've also heard of people converting them to use a Fender tank? I guess I'll start with a total recap and replace the rectifier diodes, then go from there. Is there a source for the original type of amp covering?

**soundmasterg** · 02-12-2009, 04:14 AM

With the tube complement and the plate voltage, if you change the screen voltage as I suggested, then you can get 40 to 50 watts out of it, whereas now it is about 25 watts. A bassman OT would be a good match if you do that. If you leave it as is, the a Deluxe Reverb OT may be ok, but I'd probably go for a little higher power capability myself....maybe a Vibrolux OT.

As far as I know, that covering is no longer available anywhere.

I converted my brother's to a Fender reverb tank and circuit, along with modding the complete amp. I posted all about it at the Hoffman bbs, but in brief, it can be done, but its a lot of work. The preamp should probably be redesigned and reordered as far as the various tubes locations in the amp, because you don't want the signal cutting back on itself, and it would go back and forth if you used the stock location for the reverb tubes. You also have to make a new, and taller head box. If I had to do it again, I'd just disable the reverb, build a seperate reverb amp like the Fender ones, and call it good.

Greg

**ahamay79** · 02-22-2009, 06:10 PM

Weber and Mercury both have replacement OT's for the 1484.

**scole** · 02-22-2009, 07:02 PM

wow, i found one of those in the trash. i took it to a teck and had it re-capped re-tubed. sounds real raw. the reverb even works.

**bbrownsbrick1** · 02-25-2009, 06:54 PM

these things have great "wide open" tone when cranked, don't own one personally, but have some experience with them. definitely a fan, and a solid bargain for what you get.

**KingCameron** · 03-12-2009, 09:53 PM

Verb sucks

These are great amps. I have restored two of them for local players and they can be great. I added a lot of insulation to the plate load resistors and changed many of them to clean the amp up.

As far as the verb goes....get a different amp if you want great verb. I've made the verb work in them, but its never that good.

I haven't tried using a fender tank on one.. It looked like a lot of work.

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