Ferrograph Reel Expert Help Please!

[Levente]

Hey Guys!

I thought I will do an update what is happened with this tape recorder. Attached few pictures of the power transformer section...there was a Dubilier cap 50+50uF and two 1kOhm 5W resistors together on the cap + pins. This cap was a Dietetic Dubilier really bad cap.

When I have turned the deck on after my last email, started to smoke. The resistors on this cap were so hot that it has melted one + wire attached to the cap and disconnected itself of the cap.

That is sure that this caused also some issues with some of the other caps at the amp stage, as I remember one of the EF86 tube was really bright like a light bulb.

I have decided to change all the caps were off, changed all the resistors connected to the bad caps. Plus, the resistors on all the other transformers and at the bias.

Replaced also the cap at the power stage too and the resistors exactly how it was.

Turned the unit on, no smoke. EF86s only lit up gently, EL84s are much brighter. The aluminium panel where the EL84s tubes are, gets hot, i guess it is normal, and at the EF86s are just a little warm.

I have not tested the sound yet at this stage, as I wanted to make sure that no shortage or bad electricity is going through the unit.

So far, this is what was happening. I have learned a lesson again, change+check everything before switching it on which I kinda did, but not carefully. My DMM showed me OK results on components were totally NOT okay.

Thanks again for all of your help!

[Levente]

.....to follow up my previous post.

I did the test. I have a 60 or 50 cycle hum. Not sure where this is coming from just yet. Also, something is not right as I hear a huge POP when I turn a unit off. When I turn the unit on, I count 17 seconds until the power on light bulb comes alive.....I found this also a bit odd.

V1, V2, V3---- checked with a chop stick, V1 and V2 sounds microphonic. I've swapped around the V1 and V2, same microphony happening. V1 is more glassy than the V2, at both ways around.

If don't touch the unit at all, I can hear a sound like someone is gently moving some broken glass on the floor, and same when I turn the unit off, more frequently and fading away.

I am quite new to this scenario and not sure what could cause this.

I have a few questions and I would really appreciate if you could reassure me on few things:

1. Power plug ground is connected to the 50uf+50uf cap ground pin. This doesn't need to be connected to the chassis too?

2. Can besides a bad tube or tubes cause the microphony effect? Mean if all the tubes are fine, but still creating microphony/glassy sound when I tap them? (the V1 and V2 specifically)

3. How do you check the EZ1 rectifier tube if its OK or not? I only have a DMM shall I take it to someone more pro?

Thanks guys!!

[BillDWVA]

Some answers to your questions:

1) it would be normal for the chassis and the -ve side of the power supply DC side to be grounded on a valve set with isolation transformer.
2) Valve microphony is to be expected. The EF86 pre-amp valves are very sensitive voltage amplification stages and should not be subject to mechanical shock during operation. A 'ring' or amplified noise is normal if you are going to tap them.
3) A slight amount of Mains hum will be heard from this type of amp. If the smoothing cap circuit is over-stressed or has components on their limit it is bound to be worse. Measure the AC voltage applied to rectifier anodes and DC high tension across smoothing cap.
4) The 'rustling' noise that you are hearing is possibly caused by a noisy resistor, especially in the anode circuit of one of the pre-amp valves or by a dirty switch contact or volume control pot track.
Hope this helps,
Bill

[Levente]

Hey Bill!

Thanks so much for the reply and the help.

I had rechecked everything since my last post. Resoldered the cap at the power transformer. Installed a new EZ81 rectifier tube (it got less buzzy and feels more stable). The huge buzz at the V1 and turned out to be a ground got disconnected probably from way too much movement by myself. Resoldered and it has gone.

The only thing is-and maybe this is totally normal scenario- that the Input 1 at V1 has about 5 times more gain compared to the Input 2.

Other than that, the unit started to sound really amazing. I have an old pre-recorded tape. Plays back OK, but when I recorded just now music on, at the playback, it started to whining and playing back not evenly...not all the time, but sometimes...first I thought it is the oscillator/bias but i think, it is the old tape and the residue on the pinch rolls and the heads...

will definitely need to try with a brand new head and fully cleaning the tape path.

I feel that I am very close now...and again, thanks so much for the help!

I love this site and really really enjoy reading so many great advises and infos.