Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 1blueheron on January 21, 2020, 07:09:39 am
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What is the consensus on the use of old parts in a new build? I have a lot of parts that I have pulled from amps. Is it foolish to re-use these parts or foolish not to re-use them? A glance on ebay says the old parts are worth more than the cost of new parts. Perhaps this is just for the purpose of authenticity or are they sonically superior?
For instance, should I use the vintage Blue Molded caps pictured below, or replace them with new Mallory 150 series caps?
Should these diodes be replaced with new 1n4007 diodes?
Are these resistors better than what I would buy new?
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I suggest not to use secondhand parts anywhere that their failure would be likely to cause damaging levels of fault current to flow. As you can't know what stresses they've been subject to previously.
Hence old diodes are scrap, specially the selenium one. Can you even identify them and their ratings?
And not to use the caps to couple to power tube control grids.
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I would put the power resistors in my parts bin, the caps in my safe deposit box, and throw the rest away.
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There was a period, some time ago, in which I had the ease of recovering old military equipment (which cannot be used today) and therefore I was able to stock up on old components
to avoid problems I have equipped myself with some equipment to be able to check the condition of the components that I have recovered, one thing has surprised me a lot
old electrolytic capacitors (of a good brand) which despite being from the 60s / 70s perfect both by measuring them with the capacimeter and with an ESR meter
I have to say that the best was used in those old military equipment
Franco
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Great topic. I think old parts bring money not from builders but from collectors who want to preserve the appearance of originality. I agree with Pete on the diodes, they’re cheap anyway. But I also collect specific NOS or even used parts for strategically positioned uses. Those blue molded caps are super reliable. I found a large store of black beauties and bought them up. I still check those for leakage before use and will only use older stuff in preamp / lower voltage applications and use more robust newer parts in higher voltage applications moving towards the output area. I like carbon comps in the signal path on the preamp side and metal oxide in the power supply, phase inverter and output applications as a general rule of thumb. I also think that the inefficiencies of nos / older parts are part of what makes old gear sound the way it does. Commercial builders I think are rightly cautious about this approach because higher chance of failure and the brand takes a hit. Because I build for myself and friends this is understood and I don’t have as much of a conflict
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I would keep the old tube sockets as their quality is good, sealed pots and knobs, pilot lights, fuse enclosures . Capa and resistors to the garbage.
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dispose of selenium rectifiers as hazardous waste. throw away the diodes. check the film caps for cracks and leakage & throw away cracked and/or leaky ones. keep the power resistors if they aren't discolored or show signs of heat stress. test and keep pots, sockets, test and keep transformers & chokes. throw away all electrolytic caps. recycle metal parts you won't use.
application specific pots are worth salvaging and usually a good application of de-oxit is all old pots need to restore function, that and the old shaft lube dries out making them difficult to turn.
--pete
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I'll use an old PT & OT. I'll use NOS parts. I normally don't use old parts. Exception would be when I gut and rebuild something like a Bogen PA into a guitar amp where I might use the sockets also.
With respect, Tubenit