Help with Kit 34 amp

[jiten]

Hi All,
I seem to come on only when I need help so apologies in advance.
1. I was thinking of buying a set of speakers with 4 ohm impedence instead of the usual 8 ohm. My Kit 34 instructions say that the output transformers are for 8 ohms and should not run the amp with 4 ohm for any length of time. Can someone help and explain this?
2. the right channel in my amp works intermittently. A gentle tap ( literally with a couple of fingers on the right of the amp and it works. However I noticed last night that the rear EL 34 of thee right channel was glowing a bright red after about 20 minutes and it appeared as if the whole plate was red hot. the valves are svetlanas and were replaced about 2 years ago. I will do a run of test voltages tomorrow. when it is working the sound is great.
Thanks,
Jiten.

[bob orbell]

Hi Jiten, first off, why do you want 4ohm speakers?, I have run a KAT6550 with 4-6 8 and 15 ohm speakers, it has done no harm to the amp, in fact I bought the 4ohm transformers from WAD expressively to run the 4ohm speakers, and to be honest, I changed back to the 8ohm transformers because they sounded better, so I say don't worry. Do not power your amp. up for too long again until you establish what is the cause of the red hot valve, it could be a faulty valve, or the capacitor and or the resistor that connects the valve cathode to ground, have you swapped two of the output valves over ? if so does the problem follow that valve, if it dose it is the valve. BOB

[jiten]

Dear Bob,
Thank you for your reply. I have not been able to get into the forum so have only just seen your reply.
I was thinking of getting the Monitor audio platinum speakers as they are being sold at a good price and are an upgrade on the looks as well as sound of my MA 300GX. But I can live with the GX and save the money.

The Right channel is a challenge. I found capacitor C17 to be faulty so changed it, I have measured all resistances and they are correct. The voltages are as prescribed in the build manual. The first capacitor died after a few hours. Once 'dead, there was no music but just a rustling on start up and shut down.
The second capacitor functions for a few minutes before the sound in the right channel gradually disappears. This time no rustling noise. I have swapped the valves and there is no change. The 'hot plate' issue has has not recurred.
Another interesting fact was that the connection from pin8 of valve V5 to the tag board at aR8 (for capacitor C17 ) was missing and apparently has been since I built the amp and there has been no detriment to the sound or performance. I cannot even explain that. I have now connected the lead and it is symmetrical with the Left channel at capacitor C18.

One last comment is that resistor R35 for the right channel V7 can get very hot but the joints are OK as is the resistance at 390R.

I have ordered parts to rebuild the right and Left channels with Tantalum resistors and Audionote capacitors but need to make sure that there isn't an obvious problem with the valve connection. I could do the octals for V 5-8 again if necessary.

Thank you for your help.

BTW I am not even sure when I built this but it has worked well for at least the last 10 years. The amp was re-valved about 1-2 years ago.

Jiten.

[bob orbell]

You seem to be doing the right thing with the amp, report back when you have replaced said components and let us know. I use Monitor Audio PL100 speakers with a WD 88 and yes they are fantastic, but be careful, they can sound very bright, just changing cables can make or brake the system. BOB

[jiten]

Dear Bob,
I have rebuilt all 3 the tag boards, with new components. I fired up today and the results are as follows. I have not replaced the transformer or choke or the large capacitor C%5
Choke pin 1 exp 400v actual 504v.
pin 2 408 506v.

C5 375 470v

v3 v4 pin 1 exp 125v actual151v v4 125v actual 155
pin 3 95 102 95 104
pin 6 125 182 125 154
pin 7 1.75 2.1 1.75b 2.22
pin 8 7.0v dc 8.58 7.0vdc 8.55

V5678 pin 28 v and 395/398 v. no power 0 V. Heaters working,

Help!

Many thanks.

Jiten.

[bob orbell]

Well, for a start your HT is way too high, in fact it is dangerous, the ECF 80 values can be way off target, they are renowned for it, I don't follow your last figures for V 5678, also, I don't have the KIT34 data, so hopefully someone else can help. BOB

[Richard]

Hi Jiten,

Long time, hope you're well!

Like Bob, I don't understand your voltages for valves V5/6/7/8. The choke and C5 voltages are high and there's no power.

The rest of your voltages seem to show valves V3/4 are working correctly but with higher HT, (that is, all voltages are higher as would be expected from the higher HT).

I'm guessing your El34's are not drawing current so the HT isn't being loaded so stays high, and, of course, there's no power from the amp.

Please check all the EL34 voltages and let us know. Check also the HT and ground connections to them (a missing ground connection to the cathode resistors would cause this for example) and hopefully you should find the problem.

[jiten]

Dear all, Thank you all and a big apology. I had missed a connection at one point and missed 2 wire connections to the ecf 80. Now everything is very close to normal i.e less than 10% out on voltage.
Playing well so will give all the new caps etc a chance to run in.
Thank you again for all your help and dare I say inspiration and help to take on something that is way outside my field.
Kind regards, Jiten.

[Phil Y]

Hello Jiten,

Glad to hear you have the amp going again.
I thought I would ask how the new components are sounding as some years back I tried some tantalum resistors but did not like them. Even after a good running in period, to my ear they had a glassy, forward sound to the upper midrange that was not to my taste. Bob says the PL100s can be bright sounding so this may not be a good combination.
Of course it may all be different with your ears/system but may be worth bearing in mind. I swapped them all out for Takman carbons that for me were far more natural sounding.

Regards, Phil.

[jiten]

Hi Phil,
The first impression was that the sound was flat. However after a few hours the sound is much better and warmer. I am using Monitor Audio Gold GX 300 speakers. Platinums are superior in build as well as a slightly lower bass, 28 Hz instead of 30Hz and a much higher top range 100Khz as opposed to my 40Khz.( I know hearing is well below 20Khz at this age but the high top end does make the sound better!) I will let this run in for a few days and will let you know. for what its worth, initially the sound seemed to come from the speakers but now seems to be more spatial so I hope that gets better over time. I also have a REL subwoofer and using it in conjunction does make you feel the music even when set on very low volume with a cut off frequency of 30 Hz so it does not clash with the main speakers.
The valves are telefunken ECF 80, Svetlana winged C EL 34. CD: Yamaha or arcam Delta 60 - both at least 15 years old but still working well.
Best wishes, Jiten.