Maybe a dumb question to you guys but I really want to know. Converting old Iron Ques

[jh45gun]

Messing with this Zenith phono amp conversion to a guitar amp project I have started is really getting addicting and I now plan to keep an eye out for other old iron to convert to guitar amps. I am on SS disability and do not work so the days get long and this looks like a fun way to occupy some of my time. My question is OK so I find a chassis out of something that has a decent looking power transformer and output transformer and the tubes are tubes that work good for guitar amps say 6v6 power tubes, 12ax7 or some thing equivelent for preamp tubes 5y3 or what 5u4 ect for rectifiers ect ect ect. My question is since the tubes are ok for guitar use what about the transformers. What I want to know is taking a chassis like I described and gutting it to make like a champ clone or a princeton clone ect how much does the transformers fit in. Will they work for most of these DIY projects or do have to worry about the transformers maybe not suited for the job. Or maybe the power tranny maybe ok but not the OT ect. Comments? Jim

[jh45gun]

Let me ask a different way. Ok ya find a piece of old iron and it has a working power transformer and Output transformer. The tubes are the same that are used in a guitar amp that you want to build. Say that it has a single out put tube with a octal socket so you can use a 6v6 or a 6l6 to build a champ style circuit as it has a socket for the 12ax7 too. Or it has a push pull tube set up with 2 6v6's, 6l6's ect so you want to make a Princeton or Delux clone. Is is safe to guess that since the tubes are the same you could gut it and the transformers once rewired to the clone circuit would have a good chance of working ok or would the circuit have to have the exact transformers that Fender used or Gibson if you decided to go that route.

[kctx2]

Many of those old phono/radio amps have been very succefully coverted to guitar amps. Usually, many of the early 60's type will have a PP 6v6 setup, with a 12ax7(or a 6c4) and a 12au(at)7. The later 60's seem to be more SE el84 types. The 6v6 transformer sets make great 18 watt amps.
If you can provide the model/chassis number (usually ink stamped on the chassis) it will be easier to determine your options.
Keith

[jh45gun]

Well if ya look at the board you will see a couple of post of my Zenith project I am working on now with Hasserls and some of the others here giving me help and pointers. It has 2 6v6 and a 6j5 preamp tube which I am changing to a 6 F5 for more power and a 12 ax7 which half is used for the phase inverter. I am modding that amp using pretty much the same circuit so that really does not apply to my question as I want to know if you find old iron that has the same tube layout or just the same tubes if you can figure that the stock trannys will work for the Fender style circuits with gutting and rewireing.

[BrownIsound]

Yes

[BLC]

Well, to go back to your original question; The "Old Iron"..... I love to use old transformers. I give guys an option when building custom amps, if they would like me to use "old iron" in their amps. There were thousands of hi-fi amps made back in the 50s and 60s that had great quality transformers in them. However, I have found that guitar amps generally had larger OP trannys for a given wattage. There are several books out that include chapters on working with the old transformers.....figuring out exactly what the ratios are etc. I like Zolotta's ( sp?I dont have it handy at the moment to check) books . Both 1 & 2 have ways to check out old ones and tell what they are and the primary ohms for OPs etc. I dont have #3 yet, but plan to get that one shortly. The TUT series also goes over transformers in one book, but I dont know which one at the moment. The higher end hi fi amps....Fisher, Scott, Harman Kardon, etc. generally had bigger transformers more like the guitar amps. I have used these in building clones, but have also modded amps like Fishers to use with guitar. Its fun and is a great way to save and use these great old amps.....

[Ronsonic]

Go ahead and have fun. Yes, there's no reason why the old iron won't work as long as you use it for designs that are somewhat similar and you don't get silly adding power tubes or anything.

Ron

[unklmickey]

...My question is since the tubes are ok for guitar use what about the transformers. What I want to know is taking a chassis like I described and gutting it to make like a champ clone or a princeton clone ect how much does the transformers fit in. Will they work for most of these DIY projects or do have to worry about the transformers maybe not suited for the job. Or maybe the power tranny maybe ok but not the OT ect. Comments? Jim


IMHO, if you use the iron together (BOTH the OT and PT) you should be okay.

particularly if you keep the same PS and output configuration.

if you change from a tube rectifier to SS, that will make more B+ available. so, you will be asking a bit more from both transformers, than the original circuit. but there will likely still be enough room.

if you also change from cathode to grid bias on the output, this will tax the iron even harder. the 2 changes together might be a bit risky, you really have no way of knowing if the transformers were over-rated enough in the original design.

i wouldn't get too cerebral about it though. just make sure you don't invest much in the donor chassis. then you have less at risk, if things do go wrong.

[donnyjaguar]

Surplus test equipment from the 1950s can be had for next to nothing and often yields great power transformers and other high-spec components.