View Full Version : Marantz 4400 CRT replacement by 2bp1

01-22-2013, 10:27 AM

I have a marantz 4400, the CRT is damaged, is the 50tb1, but I could be replaced using the RCA crt 2bp1, works perfect, without modifying the circuit or voltages, only changing the connector pins, attached diagram. This is achieved crt on ebay at a price of 30 dlls, is very easy to get, unlike the original which cost 300 dlls, and is very difficult to achieve, is 2 inches in diameter by 6 long. I hope to serve.

01-22-2013, 12:25 PM
:tresbon: Wow - awesome tip!! There are quite a few of us 4400 owners out there with some pretty good burn-in on our scopes. For $30-40 bucks and some minor rewiring we'd be back in business.

Thank you!

(PS>> Possible to fix your picture links so we can have a look?)

01-22-2013, 01:07 PM
Very cool....Thanks....

I have two Russian replacements.... But the RCA is cheaper and easier to get....


01-22-2013, 05:21 PM
Would the 2AP1 CRT work as well?

01-22-2013, 07:45 PM
possible, I compare the 2bp1 and have similar characteristics, but smaller diameter, attached the schematic below.

Sandy G
01-22-2013, 08:08 PM
Fair Radio Sales in Lima, Ohio USED to have a pretty good supply of 2BP1s. I haven't seen a catalog of theirs in a long time, but I'd bet they still have 'em. They catered to the ham/Burgeoning Mad Scientist crowd.. The Audiophools kinda looked down their noses at 'em, but they never knew what they were missing, IMHO..

01-22-2013, 09:17 PM
This would be good news to those who need it, maybe also works in the similar 2110 and 2130 tuners with scopes?

01-23-2013, 03:17 AM
This would be good news to those who need it, maybe also works in the similar 2110 and 2130 tuners with scopes?

Don't see why it wouldn't work. My 2110 used the 50TB1. And the 4400 is packed much tighter, so space shouldn't be an issue either.

Sam Cogley
01-23-2013, 05:00 PM guys are making me want a Marantz with a scope. :D

01-23-2013, 08:19 PM
You gots to have a scope....

01-23-2013, 08:29 PM
Scope's the shit!

01-24-2013, 05:25 PM
Updated mine but, used seperate filament transformer since the amperage requirement is much higher.

02-28-2013, 04:29 PM
> Updated mine but, used seperate filament transformer since the amperage
> requirement is much higher.

Camman: Was this reference to the 2BP1 tube Novanec refers to ?

Has anyone else tried this substitution ?

02-28-2013, 04:58 PM
I believe the 50TB1 has a 160ma heater rating vs. 600ma rating for the 2BP1.
Haven't heard of anyone smoking the stock transformer heater winding but, I decided to just be safe and add seperate 6.3v 1 amp transformer.

03-01-2013, 11:00 AM
Thank you for shooting over that response so quickly !
I have 4 questions....

1. How did you know the current requirement of the 50TB1 Filament ?

2. Did you find the 50TB1 Pinout Specs somewhere ??
If so, will you share the source?

3. I assume you used Novanec's pin out modification illustration ?

4. Now that you have done the modification, how does it compare to the original performance wise ?

03-01-2013, 11:20 AM
I looked at my files but, can't find where I saw the heater spec.
The pinout is contained in the 4400 schematic.
No, my conversion was been done 2-3 years ago.
Changed my green crt to a "russian" blue phosphor crt. Works fine but, not quite as bright.
Please no worry about questions, glad to help!

03-02-2013, 08:17 PM

these documents are of 50TB1 and 2BP1,

2BP1 =

50TB1 =

currently this modification, it works perfect, without modifying filament voltages, brightness is good, and I use the same power supply. I hope to serve the documents.

03-02-2013, 08:22 PM

I forget, the heater current for 50TB1 is 6.3v 0.3 amp and for 2BP1 6.3 v 0.6 amp..


03-06-2013, 08:39 PM
Hey Guys,
Sorry for the delay getting back to you both.
I didn't realize that there was a second page !!

Thank you both for the replies! They answered many questions.
Novanec: The pdf and gif images were GREAT and will be a great help

Camman: Yes, I have the 4400 schematic but I don't remember the pinout specs being there. Novanec's pdf helped out in this regard.

Also Camman:
How did you find a blue 2BP1 ????
I thought they were only available in green....

If you guys ever need help trouble shooting the 4400 or a 4300 I have outlined quite a number of issues on the schematic. I bought them new in 1976 and have serviced them many times over the years. If you plan to keep the receiver for the long haul, I can be reached directly: NetcomD(at)

03-06-2013, 09:41 PM
The pinout spec's I thought you referred to was the pin# and internal connection.
The blue phosphor CRT is a Russian tube 5LO38M. Very difficult to locate these days. Found mine after an arduous Internet search. :boring:

03-07-2013, 12:02 PM
Now I'm more confused than I was before!
You used a 5LO38M blue in a 4400.
Did you also use a 2BP1 in another 4400 ?

03-07-2013, 12:07 PM
I have never installed a 2BP1 in a 4400.
The "M" is the code for blue phosphor.

03-07-2013, 02:03 PM
Thanks for the clarification.