Marantz 8B Restoration

[gadget73]

Never really got that. Its worth more if original but unusable vs with caps that aren't going to destroy output tubes.

I don't run a museum, and I don't do things with notion of resale value in mind. If I can't use it, I don't want it. Those caps were lousy in the 50s and they haven't improved with time.

 

[Mr Boochie]

Never really got that. Its worth more if original but unusable vs with caps that aren't going to destroy output tubes.

I don't run a museum, and I don't do things with notion of resale value in mind. If I can't use it, I don't want it. Those caps were lousy in the 50s and they haven't improved with time.

I don't believe that, either.

The unit should be playable and safe, to fully enjoy it.

I think some of the problem can be the wholesale change to parts that can lower the unit's reliability and also alter the inherent sound of the unit. It really depends on who did the replacing and the logic behind the replacements.

The ultimate goal should be to maintain the original tone and bring the dependability up to par.

 

[trainbuftony]

I have pitched a lot of bumblebees from equipment, literally hundreds of them.
I've never had an Amp sound bad after the bumblebees are removed.
They always sound better, after and they work better too.
The old failed bumblebees can sell on eBay for enough money to cover the cost of new capacitors in many cases.
People put them in their guitars where they work OK because they aren't being asked to block direct current from a grid, and their drift just adds a level of bespoke customization...
Sell them to the guitar people and get some orange drops (from mouser) or something like that.

 

[Mr Boochie]

I have pitched a lot of bumblebees from equipment, literally hundreds of them.
I've never had an Amp sound bad after the bumblebees are removed.
They always sound better, after and they work better too.
The old failed bumblebees can sell on eBay for enough money to cover the cost of new capacitors in many cases.
People put them in their guitars where they work OK because they aren't being asked to block direct current from a grid, and their drift just adds a level of bespoke customization...
Sell them to the guitar people and get some orange drops (from mouser) or something like that.

I don't like those old-school Bumblebees. In guitars or amps.

I like the Russian (CCCP) PIO K42Y, in most guitars using alnico magnet pickups. They have that old-school warm vibe of the old Bumblebees.



BTW... I'm not a big fan of PIO coupling caps in tube amps. Unless you really make a point of keeping them away from heat.

 

[mcgjohn]

Besides heft, another reason I decided to put mine up for sale and get a recently made similar topology Mullard amp with modern components.
I have a couple of nice time capsules that please me as-is not in use, nor will be.

tend to agree.

 

[gadget73]

one of these days I'll have to get myself an 8B and make everyone's head explode by recapping it with the cheapest caps money can buy. I've got a big bag of Taiwanese ETR brand metalized polyester caps kicking around, those ought to fit the bill. I think they cost about a quarter each.

 

[rothwellaudio]

People put them in their guitars where they work OK because they aren't being asked to block direct current from a grid, and their drift just adds a level of bespoke customization...
Sell them to the guitar people...

I never understood the fetish for weird old caps in electric guitars. Most guitarists I know leave the tone controls on full anyway where the cap is effectively out of the circuit.
Gibson used to have something on their website saying that fancy tone control caps make no difference, but they seem to have given up on that idea and instead now sell fancy capacitors for guitar "upgrades".

 

[trainbuftony]

You know what they say about fools and their money...

Soon parted.

Selling your dead caps to fund working caps is the opposite of foolishness.
There's enough fools running around to fill up 3 earth's. I'm trying to help people to make better decisions and have more fun by spending money where it does the most good. I've got a fair amount of experience and I remember a time when I did not....

 

[Mr Boochie]

I never understood the fetish for weird old caps in electric guitars. Most guitarists I know leave the tone controls on full anyway where the cap is effectively out of the circuit.
Gibson used to have something on their website saying that fancy tone control caps make no difference, but they seem to have given up on that idea and instead now sell fancy capacitors for guitar "upgrades".

Guitarists are as susceptible to Net jive talk, like other "hobbyists" are. Many think, this ONE amp, this ONE guitar, this ONE mod, this ONE pedal, this ONE tube... is gonna make me sound like Stevie Ray! The crazy online shops play to those delusions.

I use the tone controls on the guitar more than the amp. It's easier, while playing. You need to setup your guitar so that the tone and volume controls are in a range that is useful. Switching caps, even if they are supposedly the same value can alter the response and control. Especially, in the guitar.

I have a couple old guitars that I haven't taken apart. There's something to be said about fooling around with the mojo of the axe. So many stories of guys changing out perfectly good pickups, strings, caps, pots on their toys. Walking away from the original tone. Then, posting on the Net, "what happened?"

 

[kstlfido]

If anyone bothered to study the schematic....

The bumblebee caps on the input of the 8B are twofold; to block DC from the input source and a low frequency subsonic filter. They typically see little to no DC voltage across them. If one is concerned about their sonics, then simply use the "Test" inputs instead, making sure your input signal is free from any DC component. The large bumblebees C15A and B in the output stage form subsonic filters in parallel with the 6.8 ohm resistors and also have next to no DC component across them.

All the other signal capacitors that do have some DC across them are Good-All 600UE. These are Mylar and of very high quality. It is very unlikely that these have failed. However, they MUST ABSOLUTELY BE CHECKED and should meet new-film capacitor specs for insulation resistance.

The under-chassis electrolytics are a different story and should be changed along with the selenium rectifier. The main filter cans are of very good quality, but MUST ABSOLUTELY BE CHECKED as well for leakage and meet new spec. I have seen these fail this test in a few 8B's that have come on my bench.

Just my 2c.

 

[ramjet]

"If anyone bothered to study the schematic...."

I did, thank you.