miklos said:For that much money, I'm sure you can buy an other machine with good heads.
Yeah, there was a nicely restored machine on eBay for about $695 recently.
The old Nortronics heads are a relative bargain, and are reputedly as good or better than the OEM heads, and have significantly better electrical performance as well.
I'm still trying to puzzle out what went awry with that head. I assume the gap has probably opened up - initially the output goes up and then drops drastically as the head finally reaches the fully worn out state. This might account for the drastic difference in output levels between the two channels if the right channel is not yet fully worn out. The groove is probably deep enough that relapping would not have given me a long term solution. Now it is no longer an issue..
I'm replacing both record and replay heads. The erase head appears completely unworn as does the rest of the tape path..
I picked up the heads this morning at the post office. The package includes everything needed to install the new heads plus rather good instructions.. I hope to do this around the end of the week.
The heads were shipped very quickly and per my instructions, they were also extraordinarily well packed.
I got them from Magnetic Head Company.. Here: http://www.magneticheadcompany.com/
I have a very vague recollection of having replaced the playback head on another G36 with a Nortronics head sometime in the early 1990s - and with very good results.
I can't wait..
Next maybe I will look for a high speed capstan and finally will think about designing a new playback amplifier around my favorite high transconductance device of the moment - the D3A triode connected..
The heads were shipped very quickly and per my instructions, they were also extraordinarily well packed.
I got them from Magnetic Head Company.. Here: http://www.magneticheadcompany.com/
I have a very vague recollection of having replaced the playback head on another G36 with a Nortronics head sometime in the early 1990s - and with very good results.
I can't wait..
Next maybe I will look for a high speed capstan and finally will think about designing a new playback amplifier around my favorite high transconductance device of the moment - the D3A triode connected..
I have definitely installed heads on one of these machines in the past.
I pulled the old heads tonight and after some very fiddly work installing the terminal clips for the new heads I installed them. I have yet to line them up or do any calibration, but the heads are physically installed.
It is a very good thing I did not send the old heads off to be relapped, unfortunately the playback head is bad. I measured the inductance after removal and the right side which is good measured 465mH and the left side measured 415mH which is well out of tolerance based on prior experience. The record head measured virtually identically on both channels at 33mH which is close to the expected value.
The QC on these heads was not the best, the epoxy encapsulant is full of voids, and tellingly the left channel of the playback head has the worst one..
Those pretty shield cans hide a multitude of sins unfortunately. The QC definitely appears to have slipped on these heads - I've never seen worse on a ReVox, and sadly there is relatively little wear to the head surfaces so they died before their time.
There also appears to be a considerable amount of corrosion (actual rust pitting) on a small area of the surface of the left channel pb head - it isn't oxide left from old tape as I originally thought. It might be a metallurgical defect or similar as there is no evidence of moisture anywhere in this machine.
I have included a picture...
I pulled the old heads tonight and after some very fiddly work installing the terminal clips for the new heads I installed them. I have yet to line them up or do any calibration, but the heads are physically installed.
It is a very good thing I did not send the old heads off to be relapped, unfortunately the playback head is bad. I measured the inductance after removal and the right side which is good measured 465mH and the left side measured 415mH which is well out of tolerance based on prior experience. The record head measured virtually identically on both channels at 33mH which is close to the expected value.
The QC on these heads was not the best, the epoxy encapsulant is full of voids, and tellingly the left channel of the playback head has the worst one..
Those pretty shield cans hide a multitude of sins unfortunately. The QC definitely appears to have slipped on these heads - I've never seen worse on a ReVox, and sadly there is relatively little wear to the head surfaces so they died before their time.
There also appears to be a considerable amount of corrosion (actual rust pitting) on a small area of the surface of the left channel pb head - it isn't oxide left from old tape as I originally thought. It might be a metallurgical defect or similar as there is no evidence of moisture anywhere in this machine.
I have included a picture...
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Here is a picture of the head assembly with the new heads installed and in the deck..
Note that the protective covers are in place until I start to do the actual alignment.
The new heads are far better than the ReVox in terms of their finish quality and build quality.
You can just see the edge of the original erase head which is still in good shape.
Note that the protective covers are in place until I start to do the actual alignment.
The new heads are far better than the ReVox in terms of their finish quality and build quality.
You can just see the edge of the original erase head which is still in good shape.
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Here is yet another picture showing the back side of the heads and the new terminal clips which are quite similar, but better quality than typical cartridge clips as they actually have small spring contacts. They are gold plated and easily soldered as long as you use a work holder or similar to do it.
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miklos said:
It's available on my G36 thread at www.tapeheads.net if you want to take a look at it now.. You would have to join first though.
The heads are trashed, very scratched although the wear grooves are not that deep. They would have been candidates for a relap under better circumstances, the gaps show no sign of opening up.
Several people have commented on other forums about how soft these heads actually are, and based on what I can see I believe it.
Here's picture of the front surface of the pb head showing the corrosion - not clearly seen is the fact that there is some actual pitting in the surface of this head. The head was carefully cleaned prior to removal, the other heads show no such discoloration, and it's NOT oxide left behind by shedding tape..
The general quality of construction of this head seems quite poor, and I am not sure why. As I have said elsewhere the shield can hide a multitude of sins, and that's particularly true in this case.
The general quality of construction of this head seems quite poor, and I am not sure why. As I have said elsewhere the shield can hide a multitude of sins, and that's particularly true in this case.
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Haven't posted much here about my ReVox G36, but I did install and align the new tapeheads and did a lot of other work on the machine.
Found and read Charlie King's "Greening of the ReVox G36" and did all of the mods outlined there and then some.
Most recently I bypassed the record input electronics and connected the radio rca input jacks directly to the record level pots. Modern digital sources produce signal levels that will overload the input amplifier under a lot of conditions.
The deck performs at least as well as my Otari when recording on Basf LPR35 at 7.5ips, and I am quite pleased with the end result.
Found and read Charlie King's "Greening of the ReVox G36" and did all of the mods outlined there and then some.
Most recently I bypassed the record input electronics and connected the radio rca input jacks directly to the record level pots. Modern digital sources produce signal levels that will overload the input amplifier under a lot of conditions.
The deck performs at least as well as my Otari when recording on Basf LPR35 at 7.5ips, and I am quite pleased with the end result.
Now i´m pretty new to the reel2reel world, but have gotten my hands on a G36 15ips version. The machine worked fine for a periode, but then one evening, when i was doing a recording, an odd smell started to appear in the room . The recording was going fine, but as i looked over to the G36 i saw smoke appear from it. I hurried to shut it of, and with a wet cloth at my side due to an apparent fire hazard 
i pulled it from the chassie to see what was going on.. the recording seemed to be going well up ontil the point when i turned it off. A closer peek on the "guts" revealed that the mains tranformer had almost caught fire, being blackenet and all bubbled up, and very very hot 
. Has any one had a similary experience, or a hint to as what the problem could be? and a good guide to dissasemble the G36, as it seems very hard to get it appart and reach the inside of the machine. And where to get a new transformer? I am planning to make a new one myself if it isn´t possible to get a new one for a reasonable price...
. The recording was going fine, but as i looked over to the G36 i saw smoke appear from it. I hurried to shut it of, and with a wet cloth at my side due to an apparent fire hazard i pulled it from the chassie to see what was going on.. the recording seemed to be going well up ontil the point when i turned it off. A closer peek on the "guts" revealed that the mains tranformer had almost caught fire, being blackenet and all bubbled up, and very very hot . Has any one had a similary experience, or a hint to as what the problem could be? and a good guide to dissasemble the G36, as it seems very hard to get it appart and reach the inside of the machine. And where to get a new transformer? I am planning to make a new one myself if it isn´t possible to get a new one for a reasonable price...
The transformer in my Revox amp went short circuit for no reason whatsoever - it was fairly new at the time too; so it's not impossible that the transformer just died. Since it was potted I couldnt repair it.
But the G36 trafo can be easily disassembled and re-wound if necessary.
But you should check the current draw on the various windings - something like an electrolytic capacitor (the 3 big cans) could have gone short circuit - or one of the selenium rectifiers - and overloaded the associated winding.
There are no secondary fuses (bad design omission! Might be something prudent to add when doing repairs).
Getting the transformer out is a major disassembly job; you have to separate the top and bottom chassis. Replacing the electrolytic caps is even more of a pain.
But the G36 trafo can be easily disassembled and re-wound if necessary.
But you should check the current draw on the various windings - something like an electrolytic capacitor (the 3 big cans) could have gone short circuit - or one of the selenium rectifiers - and overloaded the associated winding.
There are no secondary fuses (bad design omission! Might be something prudent to add when doing repairs).
Getting the transformer out is a major disassembly job; you have to separate the top and bottom chassis. Replacing the electrolytic caps is even more of a pain.
Sorry to hear about that, usually the cause of such issues is either a partial short in one of the various windings or a failing selenium rectifier or supply filter capacitor.
First thing is to get a copy of the service manual online if you do not already have it.
You'll find the last version of the service manual here: http://www.johnmcculloch.net/documents.aspx
Here is an article on restoring the G36 in addition to my writings here and at tapeheads.net
http://koti.mbnet.fi/siliconf/JukkaTolonen/ga/revox/revox.html (Note that the contact information there for JM Technical Arts is out of date.)
JM Technical Arts has a lot of spare parts for the G36 and might have transformers for your model in stock - their prices are very reasonable unlike most ePay sellers, but the shipping costs might be a bit over the top. You'll have to email them for more information - their site is here: http://www.jmtecharts.com/
You probably know this already or have just learned it the hard way, but old tube gear should not be pressed back into service without a thorough check out and some time on a variac to reform the caps before use. (Generally replacing selenium rectifiers and filter caps helps to prevent these sorts of experiences.) Even with these precautions it is not unlikely that something will go wrong, and these machines run very warm compared to more modern machines. Your's unfortunately is not the first story of this type I have heard.
Worst case rewind the existing transformer, or find a donor machine - do not throw just any old transformer in there as the magnetic fields are likely to cause problems with hum pick up in the electronics and heads..
As for disassembly the manual shows the horrible details and there are NO short cuts. Take your time, take a break any time you start to feel frustrated, and take plenty of pictures and notes as it comes apart so that you can get it back together again. Do not force anything - step back and take another look..
Alternately sell me the capstan motor.. I always wanted to experience the nightmare of converting mine to 15ips operation..
First thing is to get a copy of the service manual online if you do not already have it.
You'll find the last version of the service manual here: http://www.johnmcculloch.net/documents.aspx
Here is an article on restoring the G36 in addition to my writings here and at tapeheads.net
http://koti.mbnet.fi/siliconf/JukkaTolonen/ga/revox/revox.html (Note that the contact information there for JM Technical Arts is out of date.)
JM Technical Arts has a lot of spare parts for the G36 and might have transformers for your model in stock - their prices are very reasonable unlike most ePay sellers, but the shipping costs might be a bit over the top. You'll have to email them for more information - their site is here: http://www.jmtecharts.com/
You probably know this already or have just learned it the hard way, but old tube gear should not be pressed back into service without a thorough check out and some time on a variac to reform the caps before use. (Generally replacing selenium rectifiers and filter caps helps to prevent these sorts of experiences.) Even with these precautions it is not unlikely that something will go wrong, and these machines run very warm compared to more modern machines. Your's unfortunately is not the first story of this type I have heard.
Worst case rewind the existing transformer, or find a donor machine - do not throw just any old transformer in there as the magnetic fields are likely to cause problems with hum pick up in the electronics and heads..
As for disassembly the manual shows the horrible details and there are NO short cuts. Take your time, take a break any time you start to feel frustrated, and take plenty of pictures and notes as it comes apart so that you can get it back together again. Do not force anything - step back and take another look..
Alternately sell me the capstan motor.. I always wanted to experience the nightmare of converting mine to 15ips operation..
Thank you for your help. Yeah i have had a look on how to take things appart, and wondered hehe. I´ll try to get the transformer out whitout destroying things , and keep an eye on things, and then check the rectifiers and caps to see if they´re dead. The machine had been running well for a couple of months and came from service in a German studio, so there was no need to "bring it back to voltage". By the way, things REALLY have to go bad before you see me throwing things out, so i wouldn´t count on me sending you the motor, hehe but i´ll keep the request in mind shouldt things get that far 
I´ll put in an update on the "operation" here when i get that far.. probably after christemas. Thanks again!!
hehe. I´ll try to get the transformer out whitout destroying things , and keep an eye on things, and then check the rectifiers and caps to see if they´re dead. The machine had been running well for a couple of months and came from service in a German studio, so there was no need to "bring it back to voltage". By the way, things REALLY have to go bad before you see me throwing things out, so i wouldn´t count on me sending you the motor, hehe but i´ll keep the request in mind shouldt things get that far I´ll put in an update on the "operation" here when i get that far.. probably after christemas. Thanks again!!
Good luck on getting your deck back into working order. I would try to buy an exact replacement transformer first before embarking on a rewind - and then a professional rewinder would save you a lot of misery..
Should you decide to rewind hopefully you can count the turns on one of the windings to at least get the turns per volt ratio used in this transformer. I am not sure where you could get documentation you need.
There is a lot of wiring you will need to disconnect before you can safely separate the top and bottom halves of the chassis. I have heard of people doing this successfully - it just requires patience and more patience.. Be sure to take lots of notes and tag all of the wiring - pictures help too..
I am still amazed at just how hot these machines run, and somewhat concerned that I may also experience a similar failure soon - yours is the third I have heard about in the last few months to have this problem. Could well be that these machines are now reaching the design lifetimes of components like the varnish on the magnet wire, etc. - things we don't give much thought to.. (I know of 100 yr old tram motors that still have their original windings, but keeping them running is problematic.)
I know the original owner of my machine, and know it had low hours of use during its first 42 yrs of existence, despite this it had significant problems.. Yours probably had a lot of use coming from a studio, and I suspect the power consumption is higher running at higher speeds and with large reels - mine does run noticeably warmer with 10.5" reels - or perhaps I am imagining this..
Hopefully you will be successful and I won't be getting that capstan motor..
Should you decide to rewind hopefully you can count the turns on one of the windings to at least get the turns per volt ratio used in this transformer. I am not sure where you could get documentation you need.
There is a lot of wiring you will need to disconnect before you can safely separate the top and bottom halves of the chassis. I have heard of people doing this successfully - it just requires patience and more patience..
Be sure to take lots of notes and tag all of the wiring - pictures help too..I am still amazed at just how hot these machines run, and somewhat concerned that I may also experience a similar failure soon - yours is the third I have heard about in the last few months to have this problem. Could well be that these machines are now reaching the design lifetimes of components like the varnish on the magnet wire, etc. - things we don't give much thought to.. (I know of 100 yr old tram motors that still have their original windings, but keeping them running is problematic.)
I know the original owner of my machine, and know it had low hours of use during its first 42 yrs of existence, despite this it had significant problems.. Yours probably had a lot of use coming from a studio, and I suspect the power consumption is higher running at higher speeds and with large reels - mine does run noticeably warmer with 10.5" reels - or perhaps I am imagining this..
Hopefully you will be successful and I won't be getting that capstan motor..
I guess you could be right about the life time of the machines.. i´m considering making a new cabinet once i´ve get it up and running again, maby an upright one with no backplate so the tubes can get some air.
I know what you mean by patience, looking at all the wires..
so a digi-cam and a lot of stickers is going to be my way in. The plan is to wind the transformer my self, counting the turns as i take it apart and watching the layout. I have acces to an old winding machine, so i hope that´ll do.. by the way i see you have an 6C33C-B on your profile pic.. I have a "longterm" amp-project running, where i have winded the output transformers for a pair of those myself I´m counting on getting 12-15W SE. But for now, i think i´ll use the christemas hollyday for gathering patience, and then face the G36 around the new year. I´ll try to post some pictures along the way if anyone is interestet.
I know what you mean by patience, looking at all the wires..
so a digi-cam and a lot of stickers is going to be my way in. The plan is to wind the transformer my self, counting the turns as i take it apart and watching the layout. I have acces to an old winding machine, so i hope that´ll do.. by the way i see you have an 6C33C-B on your profile pic.. I have a "longterm" amp-project running, where i have winded the output transformers for a pair of those myself I´m counting on getting 12-15W SE. But for now, i think i´ll use the christemas hollyday for gathering patience, and then face the G36 around the new year. I´ll try to post some pictures along the way if anyone is interestet.