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4-65A Triode curves?

dshortt9 said:
Thanks for the lead. I'll try it and if I get some info I'll pass it along. Found a Mu of 5 g1 - g2 so that is in the ballpark. Might have to get one and light it up.

I am using the 4-65A at present and have traced the triode curves on the tester up to 400V . 845 curves are close enough , Ra is around the 1.6k mark , mu of 5 . Currently running mine with James 6123HS at 530V/50mA , really these need to be run at around 650V / 55mA to get some decent power . Here's a pic of the Mk1 breadboard with T20 driver , it's totally different now and has LCL DC filament supplies , I would recommend implementing DC fils with all the big Eimacs with spiral filaments such as 100TH , VT127 and 4-65A . Also don't forget the heat dissipating caps !!!!!!

cheers

316A
 

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I have a bunch of 4-125A`s, sockets and associated parts pulled from some 500 watt transmitters (FRT-501). A bank of four in parallel ended up a PWM modulator to kick a magnetron for a radar astronomy telescope. These are an attractive radiation cooled tube. When the plates are glowing orange (permitted) they look very serious.

The 4-125 is similar to the 4-65A. just twice the Pd.

I have given some thought to a SE amp using this tube, so will follow this thread with interest.
 
rcavictim said:
The 4-125 is similar to the 4-65A. just twice the Pd.

I have given some thought to a SE amp using this tube, so will follow this thread with interest.

I don't know about using the 4-125A as a tetrode but as a triode it's probably no good unless run zero bias . It will have Ra over the 2.5k mark and would require running the G2 way over it's 600V limit . Also think about the filament rquirements . I had problems getting the 4-65A quiet with AC . Tried different variations of hum pots , CT filament transformers etc and gave up and went to LCL DC filaments . The 2 x [email protected] input chokes , filament transformer and 2 x [email protected] isolation chokes added 18kg to the amp's weight .

cheers

316a
 
dshortt9 said:
I had thought of using a 4E27A/5-125B but after hearing of your hum problems it might be harder than I thought. Someone posted triode curves of this tube showing an Rp of 1200. Perhaps using a HF switching supply would help?

4E27 will have Ra around 2k as a triode . The Eimac datasheet specifies mu of 5 , gm of 2.15mA/V @ 50mA and I would expect similar as a triode at 500V . The 750V 20 watt G2 rating looks nice though :) I have no idea what switching power supplies sound like . Iron in the filament supply sounds good . I have plenty of iron but no SMPS so I'll stick to that for the time being ;) Maybe I did something silly when AC filaments were tried . Try AC anyway but make sure you use an SG240 'surgeguard' on the transformer's primary

cheers

316a
 
316a said:


I don't know about using the 4-125A as a tetrode but as a triode it's probably no good unless run zero bias . It will have Ra over the 2.5k mark and would require running the G2 way over it's 600V limit . Also think about the filament rquirements . I had problems getting the 4-65A quiet with AC . Tried different variations of hum pots , CT filament transformers etc and gave up and went to LCL DC filaments . The 2 x [email protected] input chokes , filament transformer and 2 x [email protected] isolation chokes added 18kg to the amp's weight .

cheers

316a


You are probably right that the 4-125A represens a challenge to fit into a practical audio amplifier. Of course this challenge, the journey as it were and the resulting esthetic beauty of transmitting bottles in your Hi-Fi setup are rewards some of us enjoy.

I have a pair of 450-TH`s here that just beg to be used in a monoblock subwoofer amp project! :D :smash: :smash: :smash:
 
astouffer said:
316a: How are you driving the 4-65a, choke loading the T20?

A CCS load set to 10mA was used for the T20 . Currently running 3C24 with the same loads with the output taken from the 'mu' output of the CCS . A Valab 1200H plate choke was also tried . The seller claimed -1dB @60kHz driven by a 6SN7 . I measured -1dB @ 13kHz with a 6SN7 section and much worse with the T20 so out they came ! Better off with a lower Ra driver . I'm thinking of ditching the linestage and going for a 2 stage 'integrated' : CCS'd 3C24 input stage with plate choked 316A driver DC coupled to the 4-65A .

ps If you are really considering using this valve , look up the James 6123HS output transformer . More or less a perfect match for the 4-65A and a bargian at $180 per pair ;)

cheers

316A
 
dshortt9 said:
I had thought of using a 4E27A/5-125B but after hearing of your hum problems it might be harder than I thought. Someone posted triode curves of this tube showing an Rp of 1200. Perhaps using a HF switching supply would help?

hey-Hey!!!,
I run 4E27 PP with AC filaments and it is quite quiet. 10k a-a, 560V B+ and 125 mA idle per valve, g2 is hooked to 40% tap. See the H-K 257B data sheet for some audio amp suggestions( SE even, but that's easy enough to convert to PP ).
cheers,
Douglas

This is the amp that stopped my amp building in its tracks...I think it has to GO! else I might not get anything else done....:)
 
dshortt9 said:
Hi Douglas.

Could not find the H-K 257B sheet. Tried Frank's and Vade-Mecuum.
PP should be quiet since the OT cancels the hum, I think? SE is harder obviously, and with efficient speakers becomes even tougher. I'm thinking of the Hammond 1629SEA in SEUL with CFB around 100ma and 700V. 6.5K load, 40% tap. 16ohm for CFB. Sound good?

Try hunting for the 4E27 then. I suspect that's what I searched for in the first place. I also got brass adapters turned so I could use 813 anode caps...seems like the perfect sub. All that's needed is to provide 10V instead of 5...:)
cheers,
Douglas
 

TonyTecson

diyAudio Moderator Emeritus
2003-05-29 2:57 am
Maybunga, Pasig City
Bandersnatch said:


Try hunting for the 4E27 then. I suspect that's what I searched for in the first place. I also got brass adapters turned so I could use 813 anode caps...seems like the perfect sub. All that's needed is to provide 10V instead of 5...:)
cheers,
Douglas


how about Philipps QE08/200? , i have a quad of thse tetrodes...

datasheet says that 750v plate and 3.6k a-a, a pair can do 300watts......
 
Tony said:



how about Philipps QE08/200? , i have a quad of thse tetrodes...

datasheet says that 750v plate and 3.6k a-a, a pair can do 300watts......


can it run without forced air cooling? Is it directly heated? Also the 4E27 and 813 are pentodes( well...beam tube at least ). The 4E27 and its cousin the 4E27A/5-125B have supressors.
cheers,
Douglas