Hi,
Jan,
If you can read the acid etched code just above the stem of the valve I can probably tell you in which factory and when that valve was made.
In the case of your CV2901, it's quite likely imported into the U.K.
(hence the Common Valve code number) from one of the Philips Holland factories; Heerlen, Sittard, Eindhoven...
Cheers,
Jan,
If you can read the acid etched code just above the stem of the valve I can probably tell you in which factory and when that valve was made.
In the case of your CV2901, it's quite likely imported into the U.K.
(hence the Common Valve code number) from one of the Philips Holland factories; Heerlen, Sittard, Eindhoven...
Cheers,
Hi,
I knew about that but find it rather unlikely in this case...
So I took another look at that document and by chance found what I was missing at first:
Assuming this EF86 adheres to correct coding (looks like it) :
You have the following sequence of code:
TTC = Type, Type : EF 86 (8Y) , C = Change code (batch # etc) We can ignore this. (5)
FYMW = F Factory : M.B.L.E. Bruxelles, Belgique (L)
Y Year : 1963 (3)
M Month : November (K)
W Week : Second week (2)
So : 8Y5
L3K2
I think that's all in all more likely than the first suggestion.
Even better news is that the MBLE Philips branch made about the best SQ tubes ever.
As for the one with the weak glow: if it has the 8Y prefix then it must be a EF86.
Heaters either work or they don't, right?
Cheers,
I knew about that but find it rather unlikely in this case...
So I took another look at that document and by chance found what I was missing at first:
Assuming this EF86 adheres to correct coding (looks like it) :
You have the following sequence of code:
TTC = Type, Type : EF 86 (8Y) , C = Change code (batch # etc) We can ignore this. (5)
FYMW = F Factory : M.B.L.E. Bruxelles, Belgique (L)
Y Year : 1963 (3)
M Month : November (K)
W Week : Second week (2)
So : 8Y5
L3K2
I think that's all in all more likely than the first suggestion.
Even better news is that the MBLE Philips branch made about the best SQ tubes ever.
As for the one with the weak glow: if it has the 8Y prefix then it must be a EF86.
Heaters either work or they don't, right?
Cheers,
Tube rolling
For sure, the Mullard EF86's add a great deal of detail across the entire range.
Also, I am enjoying some (now burnt in) EL34's which are supposedly made at the RFT plant in East Germany and could have been branded Siemens or Telefunken. They are currently regularly available on Ebay and are a great improvement on Golden Dragon. I have not tried Svetlana's.
For sure, the Mullard EF86's add a great deal of detail across the entire range.
Also, I am enjoying some (now burnt in) EL34's which are supposedly made at the RFT plant in East Germany and could have been branded Siemens or Telefunken. They are currently regularly available on Ebay and are a great improvement on Golden Dragon. I have not tried Svetlana's.
Reading through all these posts has made me keen to try out my home-brew 5-20s that I built close to 30 or so years ago. These amps have not been used for well over 20 years, and still have the original Mullard valves in them. Carefully blowing all the dust off them, I found to my utter disgust that one of the GZ34 rectifiers had gone to heaven, it was all white as proof thereof. Not having a spare suitable valve at hand, I hastily replaced it with a couple of 1N4007s which I had, fitted a 100 Ohm WW 10 Ressistor to each anode, and, not owning a Variac, wired a 240V 100W globe in series with each mains lead & powered up.
The globes lit up, the filaments lit up, and a faint hum was evident at the speakers. I left it like that for 30 minutes, then removed the series-globe and fired up directly to 240V AC.
The Bias voltages had strayed from where they should have been, replacing the coupling caps solved that problem. The amplifiers worked 100%.
Looking at JdeV's revamped amps has made the decision for me, I am going to strip the amplifiers down to bare bones, powder-coat the chassis (or chrome it) and rebuild the amplifiers anew with modern components. Luckily, I still have a brand new set of NOS Mullard valves (except for the GZ34 rectifiers) on hand. I also have the Mullard 4-valve stereo pre-amp for this unit, I might use this to control the amplifiers, or make use of a Quad 22 pre-amp which I also have.
Will post pics as I complete the job. I have taken the original Mullard Book (with the green cover) to the local printers for re-binding, as it is starting to become tatty.
-Eric
The globes lit up, the filaments lit up, and a faint hum was evident at the speakers. I left it like that for 30 minutes, then removed the series-globe and fired up directly to 240V AC.
The Bias voltages had strayed from where they should have been, replacing the coupling caps solved that problem. The amplifiers worked 100%.
Looking at JdeV's revamped amps has made the decision for me, I am going to strip the amplifiers down to bare bones, powder-coat the chassis (or chrome it) and rebuild the amplifiers anew with modern components. Luckily, I still have a brand new set of NOS Mullard valves (except for the GZ34 rectifiers) on hand. I also have the Mullard 4-valve stereo pre-amp for this unit, I might use this to control the amplifiers, or make use of a Quad 22 pre-amp which I also have.
Will post pics as I complete the job. I have taken the original Mullard Book (with the green cover) to the local printers for re-binding, as it is starting to become tatty.
-Eric
Family_Dog said:
Hi Eric, welcome to this forum - although you joined in May already
Good luck with your project, just ask if you are looking for high quality components. I found some good places on the NET where you can order very nice caps and resistors. That is to say if you don't know them already.
Enjoy!
Hi JDeV,
Thanks for the welcome!
I priced components today from Mantech in JHB, who are able to supply everything except for the 500V smoothing electrolytics. They do have 450V DC electrolytics. I'm not sure whether that voltage is not perhaps a bit low, though. Guess I'll fire up one of the amplifiers and just measure what the DC voltage actually is straight after the rectifier. I haven't got my manual back from the printers yet, so not sure what the schematic has to say about this voltage on the filter caps.
I also have an Adcom Preamp, might use this (solid state) unit to control the amplifiers instead of the Mullard Stereo pre-amp or the Quad 22. Decisions, decisions, decisions...
-Eric
Thanks for the welcome!
I priced components today from Mantech in JHB, who are able to supply everything except for the 500V smoothing electrolytics. They do have 450V DC electrolytics. I'm not sure whether that voltage is not perhaps a bit low, though. Guess I'll fire up one of the amplifiers and just measure what the DC voltage actually is straight after the rectifier. I haven't got my manual back from the printers yet, so not sure what the schematic has to say about this voltage on the filter caps.
I also have an Adcom Preamp, might use this (solid state) unit to control the amplifiers instead of the Mullard Stereo pre-amp or the Quad 22. Decisions, decisions, decisions...
-Eric
Hi All,
An update on my 5-20 saga. I have been running the old amplifiers with their original components, including filter caps, valves & coupling caps for a couple of days now, and they are working so well with no hiss, pops & bangs, that I am now reluctant to strip them purely for the sake of re-painting the metal chassis. I have therefore decided to leave them as they are - "if it ain't broke, don't fix it!".
I now intend to make a project of building another two 5-10 amplifiers, just to keep me busy. I am able to source all the compnents locally, with the exception of the filter electrolytics. I can, however, acquire 50uF + 50uF electrolytics rated at 500V DC. The old electrolytics are rated at 8uF @ 500V DC. I am led to believe that the GZ34 rectifier is capable of handling these larger caps. Has anyone tried using larger caps as filter caps? I will place a series resistor of about 100 Ohms in each Anode lead which will help prevent a sudden rush of current through the valves and it is my opinion that this will be satisfactory. However, I would appreciate other points of view on this.
-Eric
An update on my 5-20 saga. I have been running the old amplifiers with their original components, including filter caps, valves & coupling caps for a couple of days now, and they are working so well with no hiss, pops & bangs, that I am now reluctant to strip them purely for the sake of re-painting the metal chassis. I have therefore decided to leave them as they are - "if it ain't broke, don't fix it!".
I now intend to make a project of building another two 5-10 amplifiers, just to keep me busy. I am able to source all the compnents locally, with the exception of the filter electrolytics. I can, however, acquire 50uF + 50uF electrolytics rated at 500V DC. The old electrolytics are rated at 8uF @ 500V DC. I am led to believe that the GZ34 rectifier is capable of handling these larger caps. Has anyone tried using larger caps as filter caps? I will place a series resistor of about 100 Ohms in each Anode lead which will help prevent a sudden rush of current through the valves and it is my opinion that this will be satisfactory. However, I would appreciate other points of view on this.
-Eric
50u is getting close to the edge, but the series resistors can help, though at the expense of efficiency and regulation. If the filter is the way I recall it (a C-L-C pi filter), you'd do better losing the series resistors, paralleling the two 8 uF caps and using them as the first cap (effectively 16 uF, well within the GZ34's limits), then using your 50uF caps as the second cap. The second cap can normally be made quite large without endangering the rectifier and that's where you'll get the most benefit from cap size increase.
Hello Sy,
Thanks for your reply. Unfortunately, I am not able to get 8uF caps at the rated voltage (500V). The 8uF caps I do have are in use in the existing amplifiers.
Your point on the high series resistance makes sense. I will be running the valves at a slightly lower voltage than that specified to place a little less strain on the system as a whole. Your assumption on the C-L-C Pi-configuration is quite correct.
I might be able to get 6uF/500VDC caps, possibly use those for the first cap and stick to the 50uF cap for the second cap. I believe that should provide sufficient regualtion and it would definitely lighten the load on the GZ34.
-Eric
Thanks for your reply. Unfortunately, I am not able to get 8uF caps at the rated voltage (500V). The 8uF caps I do have are in use in the existing amplifiers.
Your point on the high series resistance makes sense. I will be running the valves at a slightly lower voltage than that specified to place a little less strain on the system as a whole. Your assumption on the C-L-C Pi-configuration is quite correct.
I might be able to get 6uF/500VDC caps, possibly use those for the first cap and stick to the 50uF cap for the second cap. I believe that should provide sufficient regualtion and it would definitely lighten the load on the GZ34.
-Eric
Family_Dog said:
Just remember electrolytic caps do dry out with time, so rather replace old ones. You get and can use (I did with great success) those polyprop (MKP) caps that you find in fluorescent light fittings and for motor starting. They come in various low values and high voltage ranges and are quit cheap also. A 6uF 250V cost only R7-00. You can get some good ones from AfCap in Randburg- http://www.afcap.co.za/
They also work very well for speaker x-over prototyping
Hi JDev,
> You get and can use (I did with great success) those polyprop (MKP) caps that you find in fluorescent light fittings and for motor starting.
Is that what you used for the filter caps? Aren't the 6uF 250V (AC?) caps rated a bit low for the voltage? I measured 475V DC on the first cap as my 5-20 warmed up. This fell to about 435V as the output valves warmed up.
I will look at the Afcap site and see what they have to offer. Thanks for the link.
-Eric
> You get and can use (I did with great success) those polyprop (MKP) caps that you find in fluorescent light fittings and for motor starting.
Is that what you used for the filter caps? Aren't the 6uF 250V (AC?) caps rated a bit low for the voltage? I measured 475V DC on the first cap as my 5-20 warmed up. This fell to about 435V as the output valves warmed up.
I will look at the Afcap site and see what they have to offer. Thanks for the link.
-Eric
Don't use 250V caps for your PSU, I just used that 1 as an example to show what you can get at what price. At least the 500V models
Hi JDev,
LOL, no, I had no intention of doing that! I have now checked over my 2nd 5-20, and although it fired up perfectly with no problems (after running it for about an hour through a 100W globe), I decided to put new decoupling Caps for the EF86 & EL34 valves anyway, seeing I have them on hand. Quite an eyeful comparing the size of the new components to that of the original electrolytics! Wonder if they'll last as long as the original Hunts Caps did. I can see when I construct the new amplifiers I am going to have to use smaller tag boards, the old ones are just too big for the size of new components!
My filter caps are as original, I don't have spares of those, but I am amazed by the absolute silence of the amplifier. I thought my speakers were O/C.
The speakers I am using for this amp are 30-year old Wharfedale Super 12s, which I agree are not anywhere near the quality of today's speakers, but, hey, it sounds good! I have other speakers which I will probably use for the new amplifiers, not sure which yet.
Great hobby, this.
-Eric
LOL, no, I had no intention of doing that! I have now checked over my 2nd 5-20, and although it fired up perfectly with no problems (after running it for about an hour through a 100W globe), I decided to put new decoupling Caps for the EF86 & EL34 valves anyway, seeing I have them on hand. Quite an eyeful comparing the size of the new components to that of the original electrolytics! Wonder if they'll last as long as the original Hunts Caps did. I can see when I construct the new amplifiers I am going to have to use smaller tag boards, the old ones are just too big for the size of new components!
My filter caps are as original, I don't have spares of those, but I am amazed by the absolute silence of the amplifier. I thought my speakers were O/C.
The speakers I am using for this amp are 30-year old Wharfedale Super 12s, which I agree are not anywhere near the quality of today's speakers, but, hey, it sounds good! I have other speakers which I will probably use for the new amplifiers, not sure which yet.
Great hobby, this.
-Eric
if you decide to get them and are looking to do a few worthwhile mods,one to consider, if you find its input sensitivity to be a bit high for a modern preamp is to convert the EF86 pentode driver stage to triode, by tying its anode and screen grid together via 100 ohm resister. there is a little more to it than that, but some of the more expereienced tube guys will know what i mean. it is also more listner friendly in this mode when usind CD players.
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