Vr 70e

Hello all,

Well I have had the amp for a few weeks now and all I can say is it's great! It sounded great out of the box with the stock valves. After about a week I brought some JAN ECF82's and JJ EL34's + Electro-harmonix 6CA7's. At first I tried the 6CA7's There was improvement over the Chinese EL34's in the midrange voices sounded far more lifelike than before, the highs sounded about the same and there was a slight reduction in the bass. Although they sounded pretty good I took them out as I noticed an increase in background hum with these. Next up is the JJ's These are by far the best out of the three, A big improvement in the mids, slight taming of the highs and the bass sounds excellent! Also no noticeable background hum with these.

Changing out the driver tube for the JAN Phillips ECF82 has improved overall clarity it adds a fair bit of detail. Also to note one of my 6F2's was microphonic so thats also an improvement.

Overall I'm very impressed with the amp it is excellent for the money.

 

Well my two amps arrived this week...........less than 7 day after ordering.

They came double boxed ....without any damage, not even a crushed corner. The finish was very good, and the cage tightly screwed down. The valves were in place and well protected with bubble wrap hoods.

The first out the box was pluged in and running ...sounded frankly poor heavy bass and recessed mid and top end. After five hours the sound had opened out consideably, checked the biasing which was good for all but one approx [308mv].

The second one was opened up, and using the schematics was checked over everything seems as specified.
So as I'm using these as power amps ....I ripped out the signal cables from pcb to vol pot to rca sockets. I then replaced the RCA with good ones [ptfe insulated types] wired these to the board with tightly twisted silver in ptfe. The removed the frankly poor input caps, just jumped the gap with silver wire. Next out were the coupling caps to be replaced with original mullard mustard caps 0.22uf 400v. Then cleaned the valve bases and pins with deoxit and then treated with progold. Now the acid test ...replaced the first one, straight away this amp sounded like it had had 5hrs running in plus the bass top end balance was much improved. After a couple of hours I checked the biasing again one was out but not a lot. So after another 5hrs or so this amp is sounding far more focused and more solid and dynamic bass.

The same was then done on the original amp, gutted and boned. In adition the feed back from the 8ohm transformer tap had a cap and resistor in parallel. These were whiped out and replaced with a dale/vishay10k 1w and a good 100pf cap. This amp was then swapped back. Consideral improvment over previous amp cleaner clearer less muddled mid bass solid and no longer one note.

mods still to do replace the prozaic 1n4007's with something that will sound better. Look at bypassing the main caps and heater supply caps, maybe add snubbers to the heated rectifier bridge.

I'm going to replace the valves at somestage i'll probabley use Hotrox as there local to me [ http://www.hotroxuk.com/store/erol.html ]
They see pretty competative price wise too.

 

I highly recommend the heater bias mod that Thorsten recommended to moi. I also prefer triode strapping the tubes and now use 5881's. I find it works much better as a power amp with a decent pre. Saying that Im getting itchy fingers for something new, oh dear.

 

can you outline the mods to the heater lines .....I think you may have told me before ! but I can find them. I wonder if they are along the same lines of thought as mine ?
I'm also thinking of doing some cap bypassing as I found a tray of 2.2uf 250v philips polypropes[?] in the reasearch and development centre [shed].

 

I may not have done actually, the email T sent me is at home and I cant remember it in enough detail, will get it later.

Ive bypassed all power caps and changed C6 (if my memory serves me correct) to the biggest MKP I could find in the research and development lab (under t'stairs).

 

BTW, you biamping?

 

Thats the idea .....swapping the pair of sonic -T's or running the valves as bass and the T-amps for the top end. As I not heard imaging and dynamics [mid and top ] like it at any but outrageous prices.

Each VR70e will run taking the same signal to both chanels ie the right channel then connecting the amps speaker outputs to the bass [L channel] and the treble[R channel]. Just to expain to those who might be unclear.

 

found those heater mods, will pm you.

What 100pf cap did you use for the feedback mod??? I had a look in the R&D room last night and they seem to be out of decent 1W resistors, will rectify soon!

 

Can't you get these in kit form too or am I confusing it with something else?

 

Getting confused, these are chinese cheapies via Germany.

Found a thread about the heater mod, read this:

https://www.audio-forums.com/as-rediect/showthread.php?t=9876