farfisa fr40 - need help

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Yvan44
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Re: farfisa fr40 - need help

Post by Yvan44 » Wed May 09, 2018 8:53 am

Hi Oid,
oid wrote:
Tue May 08, 2018 11:12 pm

We need these resistances, power tubes pulled and speakers disconnected.
1 to 2 142 ohms
2 to 3 192 ohms
1 to 3 335 ohms
4 to 5
5 to 6
4 to 6
1 to 2 142 ohms
2 to 3 192 ohms
1 to 3 335 ohms
4 to 5 0.3
5 to 6 0.4
4 to 6 0.7

1 to ground >40M ohms
2 to ground >40M ohms
3 to ground >40M ohms
4 to ground 190k ohms
5 to ground 190k ohms
4 to ground 190k ohms

A small isolation pb on the speaker side, but this should be OK, don't you agree?
Do these same reading between the 4 leads of the reverb transformer with the tank disconnected and the ECL86 pulled.
reverb tank : pin 1 - 2
1 to 2 0.6 ohms
3 to 4 380 ohms

1 to ground >40M ohms
2 to ground >40M ohms
3 to ground 20M ohms
4 to ground 18M ohms

Does it look good to you?

Regards

Yvan

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oid
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Re: farfisa fr40 - need help

Post by oid » Sun May 13, 2018 1:26 am

Things got a little busy for me this past week.

The secondary seems abit low but not necessarily bad, would need to do some math to refresh my memory.

I think you need to get some fuses and new power tubes. Power it up with a new fuse and no power tubes, see if the fuse blows, if not try it with the power tubes (speakers or dummy load connected!) and see what happens.

2 Amp Slow Blow should be about right, but I do not have time right now to do the math and figure out the amps actual consumption, almost all amps have the value listed by or on the fuse holder though.

While waiting for the fuses/tubes double check your work on the recapping and check the value of all of the resistors in the power amp and any components which connect directly to the HT supply, anode resistors and any caps, and replace that power chord with a proper grounded chord!
Logic gates based on billiard-ball computer designs have also been made to operate using live soldier crabs of the species Mictyris guinotae in place of the billiard balls.

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Yvan44
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Re: farfisa fr40 - need help

Post by Yvan44 » Sun May 13, 2018 12:47 pm

Hi Oid,

Thanks for your reply.

On my side, I had a long week-end and
- first : I really regret that I 've not read this post first : Troubleshooting an amp? Read this before you post your ques :
viewtopic.php?f=43&t=14794
I'm very sorry about it as I've found many answers to my first questions, I've learn a lot of things about tubes - even if I'm got a electronics engineer diploma 20 years ago...Too bad that I've didn't find this topic first.
- manage to get a EZ81 tube (Dario miniwatt) - NOS

So I've just came back home since two hours : rebuilt the power cord with ground and fuse (1A). Power up the amp with a new EZ81 without the EL34, wait about 1mn... no pb, then power up with all tubes, wait about 1mn... no pb, plug a guitar, and sound comes!!! :)

So it's up and running now, sound is quitte good, but some scratch noises. Well I've some more questions, so I'll open a new thread in the appropriate section.

So thanks for your help. First step OK!

Regards
Yvan

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