jayjay1024 Posted August 3, 2023 Posted August 3, 2023 On 17/12/2022 at 5:47 AM, option-up said: Hi John, I sold that amp some time ago, and just moved on. Since it was my introduction to hifi and valve amps, I decided not to mod it but just sell it on and move up the chain. I now have a single ended KT150 tube amp that I love (although I don't think that will be my last ever amp either). But, back to 5BK7As. I bought a few off eBay - they can be found quite cheaply, if you search. But you are buying blindly (e.g. no matched pairs, but they are usually guaranteed to at least be working). I bought about a dozen and used a basic tube tester (all covered above in this thread) and ended up with about 3 closely matched pairs (the likes of CBS, RCA branded ones). And just rolled and listened and learned. And then moved on. Good luck! so how did the RCA branded ones compare to the stock GE ones?
option-up Posted August 4, 2023 Author Posted August 4, 2023 To be honest, I don't remember hearing much of an improvement. When I switched power tubes from Electro Harmonix EL34s to Genalex Gold Lion KT77s, then I heard a decent improvement - better bass, mostly.
Angelof Posted January 15 Posted January 15 (edited) Ciao, sono nuovo qui, ho scoperto questo forum mentre cercavo valvole di ricambio per le 5BK7A, devo dire che ho contattato il produttore su Aliexpress Cina e mi hanno offerto di acquistare un set nuovo e testato di queste valvole al prezzo di 130 dollari americani, il che mi sembra giusto, tuttavia ritengo che quelle valvole preamplificatrici abbiano una durata molto lunga (5000 ore) in quanto sono a basso consumo, quindi ho capito che in effetti non era utile cambiarle Edited January 15 by Angelof
option-up Posted January 15 Author Posted January 15 (edited) The stock 5BK7A tubes were made by GE, so you would assume they were pretty good. I could buy NOS tubes for as little as $5 USD on eBay, if I remember rightly (this was over 3 years ago), but only about half of them tested as good. So replacing the tubes was more for the fun of trying out tube rolling. Edited January 15 by option-up 1
muon* Posted January 15 Posted January 15 1 hour ago, Angelof said: Ciao, sono nuovo qui, ho scoperto questo forum mentre cercavo valvole di ricambio per le 5BK7A, devo dire che ho contattato il produttore su Aliexpress Cina e mi hanno offerto di acquistare un set nuovo e testato di queste valvole al prezzo di 130 dollari americani, il che mi sembra giusto, tuttavia ritengo che quelle valvole preamplificatrici abbiano una durata molto lunga (5000 ore) in quanto sono a basso consumo, quindi ho capito che in effetti non era utile cambiarle https://translate.google.com/ Hi, I'm new here, I discovered this forum while looking for replacement tubes for the 5BK7A, I have to say that I contacted the manufacturer on Aliexpress China and they offered to buy a new and tested set of these tubes for the price of 130 USD, which seems fair to me, however I believe that those preamp tubes have a very long life (5000 hours) as they are low consumption, so I understood that in fact it was not useful to change them
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