Anyone using KT88's in D series ARC gear?

Hi, I just bought an original ARC D-70 (which is currently down.:0(
Anyhow, I own a matched quad set of Golden Aero KT88's that are like new.
Is it possible to substitute these for the 6550's in the D-70?
Anyone running KT88's instead of 6550's in their older ARC gear?
Also, i am having a problem with my speaker cables as they are terminated with spades and won't fit the original ARC speaker terminals, any suggestions?

It has been a long time since I owned my D70. ARC amps of that period have a limited range on their bias pots. So the answer is without modification, maybe. Turn the bias pots down and install the KT88s. See if you can turn the trim pots to the proper bias. I never tried KT88s in my D70. I did run them in my Classic 60 and a slight modifications needed to be made so that they could be biased.

The Speaker strips were always a problem. Though I think spades have gotten a little bigger over time. I used Audio Research speaker cables with my D70 so I had no problem. Excellent cables for the money with ARC equipment.

How are the 2 large Capacitors? If they have not been replaced they should be checked. They may need to be replaced soon.
Hi Lostbears, Thanks for the input. I think the two large Caps may need replacement as they are all original. The speaker strips seem designed for bare wire or? Anyhow, like you say they are a real problem. I will probably have someone replace those along with the cheap RCA's and the hardwired power cord.
Audio Research offered an upgrade to the Classic Series amplifiers which replaced 6550 output tubes with KT88 tubes. I believe the change over required a resister replacement in order to properly use the KT88 tube.

I would not change anything in your D-70 if it is not broken. I have owned ARC equipment much older than the D-70 which were still operating perfectly.

The barrier strips are not a problem. You just need the proper spades to fit the barrier strips. Why would you change the amp instead of the cable connectors?

The power cord is hardwired for a reason. It is a solid connection and the power cord was voiced by ARC for your amplifier.

The RCA connectors are not cheap. ARC used those connectors for years on some of the best sounding equipment ever made until the Tiffany style connectors came along. I have never heard of anyone complain about those connectors on a D-79B and I doubt that anyone has ever changed the power cord or barrier strip on that amp either.

You will only degrade the D-70 by making any changes. Buy some 6550s and enjoy the amp the way it was intended to be used. They will cost less than making the changes you mentioned.

Check around for smaller spades. I know someone like Audioquest or Cardas makes them.

I agree with Rrog, The amp is a classic and I wouldn't change anything on it. I would have the caps checked because they can leak when they get old. You said that it is currently down. Instead of spending money to modify it. I would consider sending it to Audio Research to have it fixed. They will go over everything and bring it back to the original specs. Put a set of new tubes reputable dealer in it first. That way ARC will not have to replace tubes. I sent my V70 in a while back and I was amazed at how good it sounded when it came back.

To replace the captive power cord with a IEC socket might be difficult. There in probably not enough clearance between the case and the board.

There are some speaker cables with smaller spades or you can replace the spades with smaller ones. As I mentioned I used and still do use Audio Research speaker cables. They are really nice cables and can be picked up used for not a lot of money. The spades will fit between the dividers on the strip.

Hi Lostbears and Rrog, Thanks for the info. I think it is wise not to modify the amp after what you have said. I too believe the amp is truly a classic and I agree with what you are saying.
I may send it to ARC for the repairs, although they are very pricey, so IF I can find a very good local tech who is familiar with these amps, I would prefer to go that way.
The smaller spades required for the speaker cable are proving a little more challenging, But hopefully I can find a supplier of these. Again thanks for the help.

I recommend using ARC for repairs and maintenance. It may cost a little more, but it will be done right. You will never know the true sound of your amplifier if it is not set up properly.
Hello Davey,
For starters, Gold Lion KT88s do not fit inside the ARC D-70 tube cage, the tube bottles are too fat.
Vampire makes spades sized for barrier strips. I believe the part # is Bar-8.
You may also want to search Banana Spade plug Adapter.
Good luck
I've had my D70s with Svetlanas for quite a while. I did think about going to KT88s but the amps worked fine so why mess with them?

However, I did have the amps modified with five way binding posts soldered to the 16 ohm outputs.

It was a much better solution since most cables that I own nowadays use bananas instead of spades.

I just sold one of them and got a pretty good price so the modification with the five binding posts did not impact the resale price, if anything it helped because the amp is much more user friendly WITH NO DEGRADATION OF SOUND!!!!

Besides, those small barrier strips would not even fit Kimber 4TC, nevermind anything bigger.
Hi Esporma, I solved the barrier strip problem by using bi-wire pairs of Nordost Red Dawn. The Nordost factory terminated the amp end with a narrow spade that works well with the ARC. BTW, I still believe that these amps are a PHENOM
BARGAIN at the price that they are selling for currently. No other amp or even any other piece of kit even comes close to this kind of a deal. I really do NOT understand why these amps are frankly been given away at this time.