Fake valves

[spendorman]

Can you provide links?

It was a few years ago, so no.

[Barry]

Some interesting stuff here

http://sound.whsites.net/fake/counterfeit-p1.htm

Ah - just read this. I take back my scepticism about fake Motorola TO-3 packaged power transistors. Still begs the question why go to all that trouble?


Fortunately I have loads of genuine Motorola 2N3055 devices knocking about here to support the several Quad 303 and 50E amplifiers of mine.

[spendorman]

Ah - just read this. I take back my scepticism about fake Motorola TO-3 packaged power transistors. Still begs the question why go to all that trouble?


Fortunately I have loads of genuine Motorola 2N3055 devices knocking about here to support the several Quad 303 and 50E amplifiers of mine.

I have a load of genuine Motorola 2N5055H, but have just discovered that they are not really a direct replacement for the RCA 38494.

See the capacitance test here. I have just done that test on mine.

http://www.amplabs.co.uk/quad%20303%20parts.htm

[spendorman]

Yesterday I ordered one of these, I expect that it will pass the capacitance test.

https://www.ebay.co.uk/itm/38494-RCA...C/311459653603

This historically has been a reliable supplier

[Barry]

I have a load of genuine Motorola 2N5055H, but have just discovered that they are not really a direct replacement for the RCA 38494.

See the capacitance test here. I have just done that test on mine.

http://www.amplabs.co.uk/quad%20303%20parts.htm

Why does the article (and others) go on about Motorola MJ15003 devices? I'm talking about 2N3055s, which Quad themselves have stated as being the device used as the third part of the output 'triple'.

What Cob did you measure on your Motorola 2N3055s?

[spendorman]

Why does the article (and others) go on about Motorola MJ15003 devices? I'm talking about 2N3055s, which Quad themselves have stated as being the device used as the third part of the output 'triple'.

What Cob did you measure on your Motorola 2N3055s?

The early 2N3055 were Hometaxial, so high capacitance (low ft) like the 34994, so OK.

Later 2N3055 were Epitaxial, so low capacitance (high ft), so not really suitable for 303.

My Genuine Motorola 2N3055's gave similar low capacitance reading to the "fake Transistor" shown in their picture (Amp Labs).

I guess that the MJ15003 is a good "modern" transistor that could be used apart from the low capacitance.

I have repaired one of my amps using a single Motorola 2N3055H and although low capacitance, I didn't get any oscillation when checked with a scope and sig gen. Perhaps just lucky.

[Barry]

I've been doing a bit of research on this.

According to Quad's 303 Service data, the final output transistors (Tr1 and Tr2) are either 2N3055 or (RCA) 38494 for amplifiers having serial numbers up to 11500, and 38494 devices thereafter.

This would tally with the later 2N3055 being epitaxial devices. It would seem that Motorola (and also RCA) moved to epitaxial fabrication to achieve faster devices, but also to increase yield.

Of the Motorola MJ15003, whilst I have to believe the Amplabs report concerning supersonic parasitic oscillation, two companies which concern themselves with Quad 303 upgrade and repair (Quad Spot and Dada), do not report any problems in using 15003 devices and in fact Dada prefer the 15003 to the 2N3055/38494.

Genuine RCA 38494 devices can be obtained them from Langarex https://www.langrex.co.uk/products/3...-303-amps-etc/, though I don't know how they ascertain provenance. Perhaps they measure the C_ob.



Whilst I have been aware of the existance of fake and counterfeit valves for many years now, learning of fake and counterfeit transistors is new to me and somewhat shocking news!

[spendorman]

Genuine RCA 38494 devices can be obtained them from Langarex https://www.langrex.co.uk/products/3...-303-amps-etc/, though I don't know how they ascertain provenance. Perhaps they measure the C_ob.

My new 38494 arrives from Langrex next week, I'll measure the capacitance.

[spendorman]

I have four 303's, thought I'd take a look at the latest production one's power transistors, probably from the mid to late 80's. IEC mains socket.

DSCF1030 by A60man, on Flickr

[Barry]

I have four 303's, thought I'd take a look at the latest production one's power transistors, probably from the mid to late 80's. IEC mains socket.

DSCF1030 by A60man, on Flickr

Yes - that concurs with what I quoted from Quad's 303 Service Data: all 303s with serial number 11500 and above were fitted with RCA 38494s. If it is fitted with an IEC mains socket it will have a SN > 80500. The serial number should be stamped on a small plate on the underside and towards the rear of the amp.

I have two 303s (one is a 303K, that is one where all the connectors are replaced by XLR types, including the mains connector). However they are packed away at the moment and I can't be bothered to get them out to have a look at their SNs, let alone open them up to inspect the power transistors.

I admire your diligence in this matter, and ask did you buy a new 38494 to replace a damaged one in one of your four 303s?